Change airbnb eslint config package to `eslint-config-airbnb-base` and update plugins.

Change `airbnb` to `airbnb-base` for .eslintrc `extends` value.

Added changelog entry

Made sure all plugins and envs are set

Corrected new failing specs

Fix blob controller spec failure

See merge request !7814

Fix typos in Bitbucket integration docs

[ci skip]

See merge request !7823

Add setting to enable/disable HTML emails

Closes #24880

See merge request !7749

Add issue search slash command

See merge request !7752

Homogenize sort and filter dropdown toggles

## What does this MR do?

Homogenizes the style of *filter* and *sort* dropdown toggles (aka buttons) related to:
- *issues* (index, new & edit views)
- *issue boards* (index);
- *merge requests* (index, new, edit);
- *projects* (index and "explore");
- *projects admin* (index);
- *groups* (show and "explore");
- *groups admin* (index);
- *users admin* (index);
- *todos* (index);
- *branches* (index);
- *commits* (index);
- *cycle analytics*;
- *network*;
- *forks*;
- *tags* (index);
- *global search*

Some other dropdowns are incidently concerned:
- project admin (show);
- assigne/due date/milestone/label dropdowns on the issue and board sidebars;
- stage dropdown on the build sidebar;
- merge request and comparison dropdowns for choosing forks and branches;
- ref switcher (e.g. in the blob (show) view or in the graphs view);

Dropdown toggles concerned by #24150 but not covered in this MR:
- Dropdowns for selection MR versions to be compared (in the "Changes" tab of an MR);
- Dropdowns that bring up a list of actions:
  - "Settings" dropdowns (such as the one found on the upper-right corner of all project pages);
  - The download/action/notifications buttons on the main project page;
  - Dropdowns located inside of list items (on list of pipelines, users and groups, for instance);
  - The "Options" button on the commit (show) view;
  - The "+" button on the tree explorer (for creating files, branches, tags, ...)

### TODO
- [ ] Update ui.html if needed

## Are there points in the code the reviewer needs to double check?

Am I changing any other dropdown toggle than listed above?

## Why was this MR needed?

For #24150

## Screenshots (if relevant)

### Issue Index

**Before:**
![issue-index-before](/uploads/1aa358b0b9e79fd3a7467b57cd2b03ec/issue-index-before.png)

**After:**
![issue-index-after](/uploads/7a4159e8927d456ed3f4390072174e49/issue-index-after.png)

### Issue New

**Before:**
![issue-new-before](/uploads/fcfb9c39d2ff8f00827f52d60db5c114/issue-new-before.png)

**After:**
![issue-new-after](/uploads/a0b151d257d8f3e8f98a2873427362ee/issue-new-after.png)

### Merge Request Branch Selector

**Before:**
![merge-request-new-before](/uploads/8dd7b6e8ea38af7aced743386bfb83ca/merge-request-new-before.png)

**After:**
![merge-request-new-after](/uploads/38ad8f5a315344b3bab7e936a84acf7e/merge-request-new-after.png)

### Global Search
![global-search-after](/uploads/f2912b7d91fd286028cb9481d2d53a82/global-search-after.png)

### Cycle Analytics
![cycle-analytics-after](/uploads/248d5ca360bb510aa0f0bfa8a1a00aae/cycle-analytics-after.png)


## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - ~~Added for this feature/bug~~
  - [ ] All builds are passing
- ~~Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)~~
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

#24150

See merge request !7583

Hide project variables values by default

Add a button to reveal/hide the values to help prevent accidental disclosure of sensitive information from wandering on a page.

![hide-vars](/uploads/5b5eeef9b4650776b529b780998bbb1b/hide-vars.gif)    

Closes #21358

See merge request !7731

Refactor issuable description and metadata form sections

Continuation of https://gitlab.com/gitlab-org/gitlab-ce/issues/23864.

Brother of gitlab-org/gitlab-ee!916.

See merge request !7758

Add diff hunks to notification emails

Add diff hunks to notification emails. Continued from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5855 - thanks @hoopes!

This also fixes an issue where the + / - prefixes were missing from diffs in emails.

Screenshots (from my browser) of the HTML emails, along with text screenshots 

![image](/uploads/cb31400becf5149d40c8bb98a655aa93/image.png)

```
New comment for Merge Request !1 on app/views/admin/builds/index.html.haml:

http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/1#note_1023

>          Finished

This is a comment at the top of a match section.
```

![image](/uploads/704dd3845797530697a27f5c1953c053/image.png)

```
New comment for Merge Request !1 on app/views/admin/builds/index.html.haml:

http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/1#note_1022

>          Finished
>          %span.badge.js-running-count= @all_builds.finished.count(:id)
>  
> -    %li{class: ('active' if @scope == 'all')}
> -      = link_to admin_builds_path(scope: :all) do
> -        All
> -        %span.badge.js-totalbuilds-count= @all_builds.count(:id)
> -
>  .gray-content-block
>    #{(@scope || 'running').capitalize} builds
>  

This is a comment at the bottom of a match section.
```

![image](/uploads/4063f3d9738aea8ebf3c0e690d0eddee/image.png)

```
New comment for Merge Request !1 on app/views/admin/builds/index.html.haml:

http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/1#note_1024

>          = link_to 'Cancel all', cancel_all_admin_builds_path, data: { confirm: 'Are you sure?' }, class: 'btn btn-danger', method: :post
>  
>    %ul.center-top-menu
> -    %li{class: ('active' if @scope.nil?)}
> +    %li{class: ('active' if @scope == 'all')}
>        = link_to admin_builds_path do
> +        All

This is a comment with some deleted and added lines above it.
```

Closes #21027, closes #24340.

See merge request !7660

Replace issue access checks with use of IssuableFinder

Split from !2024 to partially solve https://gitlab.com/gitlab-org/gitlab-ce/issues/23867

## Which fixes are in this MR?

 - Potentially untested  
 - No test coverage  
 - Test coverage of some sort exists (a test failed when error raised)  
 - Test coverage of return value (a test failed when nil used)  
 - Permissions check tested

### Issue lookup with access check

Using `visible_to_user` likely makes these security issues too. See [Code smells](#code-smells).

- [x]  app/finders/notes_finder.rb:15 [`visible_to_user`]
- [x]  app/views/layouts/nav/_project.html.haml:73 [`visible_to_user`] [`.count`]
- [x]  app/services/merge_requests/build_service.rb:84 [`issue.try(:confidential?)`]
- [x]  lib/api/issues.rb:112 [`visible_to_user`]
  - CHANGELOG: Prevented API returning issues set to 'Only team members' to everyone
- [x]  lib/api/helpers.rb:126 [`can?(current_user, :read_issue, issue)`] Maybe here too?
- [x]  lib/gitlab/search_results.rb:53 [`visible_to_user`]

### Previous discussions
- [ ] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#b2ff264eddf9819d7693c14ae213d941494fe2b3_128_126
- [ ] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#7b6375270d22f880bdcb085e47b519b426a5c6c7_87_87

See merge request !2031

Fix missing access checks on issue lookup using IssuableFinder

Split from !2024 to partially solve https://gitlab.com/gitlab-org/gitlab-ce/issues/23867

 - Potentially untested
 - No test coverage
 - Test coverage of some sort exists (a test failed when error raised)
 - Test coverage of return value (a test failed when nil used)
 - Permissions check tested

- [x]  app/controllers/projects/branches_controller.rb:39
  - `before_action :authorize_push_code!` helpes limit/prevent exploitation. Always checks for reporter access so fine with
    confidential issues, issues only visible to team, etc.
- [x]  app/models/cycle_analytics/summary.rb:9 [`.count`]
- [x]  app/controllers/projects/todos_controller.rb:19

- [x] Potential double render in app/controllers/projects/todos_controller.rb

- https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#cedccb227af9bfdf88802767cb58d43c2b977439_24_24

See merge request !2030

Fix information disclosure in `Projects::BlobController#update`

It was possible to discover private project names by modifying `from_merge_request`parameter in `Projects::BlobController#update`. This fixes that.

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

https://gitlab.com/gitlab-org/gitlab-ce/issues/22869

See merge request !2023

Fix label creation non members

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23416

See merge request !2006

Remove `memberOf` OID in LDAP `user_filter` docs

While not technically invalid, it is not necessary to have the 
`memberOf` OID in the `user_filter`. It clutters things up and causes
confusion for users so it's better if we remove it from the docs.

See merge request !7809

While not technically invalid, it is not necessary to have the 
`memberOf` OID in the `user_filter`. It clutters things up and causes
confusion for users so it's better if we remove it from the docs. 

Create secondary colors for buttons with SCSS functions [Proper]

## What does this MR do?
* Removes the hardcoded values for button colors and generates them using the `darken` function
* Adds a border color for outline buttons on hover, focus and active states
* Adds darker colors for outline buttons in their active state

## Are there points in the code the reviewer needs to double check?
Naming for new factor variables might not be good enough.

## Why was this MR needed?
Increases visibility of alternate states as specified in #24145

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #24145

See merge request !7797

Signed-off-by: David Wagner <david@marvid.fr>

Apart from Issues and Merge Requests pages, there are other sort/filter
dropdowns that needed updating.

Signed-off-by: David Wagner <david@marvid.fr>

[ci skip]

Signed-off-by: David Wagner <david@marvid.fr>

The chevron now has the same darker shade when the dropdown is opened it
had when hovered on.

Signed-off-by: David Wagner <david@marvid.fr>

Make sort and filter dropdowns look the same and tweak their icon and
colors according to #24150.

Signed-off-by: David Wagner <david@marvid.fr>

This new global setting will allow admins to specify if HTML emails should be sent or not,
this is basically useful when system administrators want to save some disk space by avoiding
emails in HTML format and using only the Plain Text version.

Add hover state to navigation rows

## What does this MR do?
Adds hover states to navigations rows

## Screenshots (if relevant)
![Screen_Recording_2016-11-28_at_09.21_AM](/uploads/5d273f8bc53f46f9b55590f56f2287d8/Screen_Recording_2016-11-28_at_09.21_AM.gif)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #24149

See merge request !7584

Adds spinner class

## What does this MR do?
Adds class to  spinner icon to actually spin.

## Does this MR meet the acceptance criteria?
- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #24985

See merge request !7761

Ensure user is authenticated to create a new snippet

Closes #25026

See merge request !7786

In the browser, we remove the + and - signs from the front of a diff
line because we add them in with CSS, so they aren't copied. We can't do
that in an email, because the CSS isn't supported, so we should keep
them in that case.

Add guidelines in doc linking with HAML

## What does this MR do?

Add guidelines and examples of HAML links to
the buil-in help GitLab exposes under /help.

See merge request !7798

Replace static fixture for zen_mode_spec

## What does this MR do?

Replace `zen_mode.html.haml` for `zen_mode_spec.js` by already existing dynamically generated fixture.

## What are the relevant issue numbers?

#24753

See merge request !7686

[ci skip]