Pass sprockets context and environment to Sass::Engine.
Always use DiscourseSassImporter, add optional sprockets deps tracking.
Get rid of plugins.css, inject it using DiscourseSassImporter.
Upgrade Onebox gem to get many new fixes
Remove unused SiteSetting
Adds a Site Setting to whitelist onebox domains
Merge pull request #2244 from vikhyat/css-import

Site Customization @import fixes