Merge branch 'refactor-header' into 'master'

app/assets/images/logo-black.png

app/assets/images/logo-white.png

app/assets/stylesheets/sections/header.scss

app/assets/stylesheets/themes/dark-theme.scss

app/assets/stylesheets/themes/ui_basic.scss

app/assets/stylesheets/themes/ui_color.scss

app/assets/stylesheets/themes/ui_gray.scss

app/assets/stylesheets/themes/ui_mars.scss

app/assets/stylesheets/themes/ui_modern.scss

app/helpers/appearances_helper.rb

app/views/layouts/_head_panel.html.haml

app/views/layouts/_public_head_panel.html.haml

app/views/layouts/admin.html.haml

app/views/layouts/application.html.haml

app/views/layouts/errors.html.haml

app/views/layouts/explore.html.haml

app/views/layouts/group.html.haml

app/views/layouts/navless.html.haml

app/views/layouts/profile.html.haml

app/views/layouts/project_settings.html.haml