fix bug 1034189 - remove notifications app.

The app is a left over from before django-tidings replaced it.
bug 1065965 - Ensure save buttons enable when CKEditor source is edited.
Bug 1070001 - Reorg Stylus - Activity

Moved .activity into its own file and changing class names to reflect component structure.

Also removed .actions reference from API key page (there were two different uses for the .actions class, but turns out it wasn't doing anything on API page, so re-styled that page to use a different component).

Pages to test (you will have to create some API keys):
https://developer-local.allizom.org/en-US/profiles/stephaniehobson
https://developer-local.allizom.org/en-US/users/account/keys
Bug 1070001 - Reorg Stylus - Light Background

Convert all instances of #f4f7f8 into $light-background-color.
Merge pull request #2802 from jezdez/bug1034189

fix bug 1034189 - remove notifications app.
Merge pull request #2781 from stephaniehobson/BUG-1070001-reorg-stylus-activity

Bug 1070001: Re-org Stylus - Activity
Merge pull request #2807 from stephaniehobson/BUG-1070001-reorg-stylus-light-background

Bug 1070001: Reorg Stylus - Light Background
fix bug 1080001 - Address New Relic-reported JS Errors
Merge pull request #2804 from darkwing/fix-source-ckeditor

bug 1065965 - Ensure save buttons enable when CKEditor source is edited.
Merge pull request #2809 from darkwing/newrelic-js

fix bug 1080001 - Address New Relic-reported JS Errors
bug 1055078 - Add JSHint to dev machines
bug 1055078 - Make analytics.js pass jshint
bug 1055078 - Make auth.js pass jshint
bug 1055078 - Make badges.js pass jshint
bug 1055078 - Make components.js pass jshint
bug 1055078 - Make main.js pass jshint
bug 1055078 - Make promote.js pass jshint
bug 1055078 - Make search-navigator.js pass jshint
bug 1055078 - Make wiki.js pass jshint
bug 1055078 - Move selectivizr to allow jshint'ing on entire directory