This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
* Update sass-rails.
* FIX: Tilt dependency has been removed from Ember::Handlebars::Template.
* Update `DiscourseIIFE` to new Sprockets API.
* `Rails.application.assets` returns `nil` in production.
* Move sprockets-rails out of the assets group.
* Pin ember-rails to 0.18.5 which works with Sprockets 3.x.
* Update sprockets to 3.6.0.
* Make `DiscourseSassCompiler` work with Sprockets 3.
* Use `Sass::Rails::SassImporterGlobbing` instead of haxxing our own.
* Moneky patch so that we don't add dependencies for our custom css.
* FIX: Missing class.
* Upgrade ember-handlebars-template.
* FIX: require path needs to share the same root as the folder's path.
* Bump discourse-qunit-rails.
* Update ember-template-compiler.js to 1.12.2.
* `prepend` is private in Ruby 2.0.0.
