Merge branch 'tidy-up-pipeline-js' into 'master'

Tidied up pipelines.js.es6 and removed jQuery where acceptable.

## What does this MR do?

A week or so ago, I made some changes to `pipeline.js` as it was a single function and we now needed to expand on the JS logic for pipelines. I decided to turn it into `class Pipelines` of `pipelines.js.es6`. To avoid review confusion I held back from changing the pre-existing function so it dealt with instance members. Every time you click the button it would re-query all the elements it needed, now its a class it doesn't need that as we can store the required elements on construction.

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

## Why was this MR needed?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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?

See merge request !6950