Implement redesign, refactor everything

- Write CSS for everything, update templates.
- Refactor discussion view. Stream is split into two components
(content and scrubber) which have their own responsibilities.
- Extract pane functionality into a mixin.
- Implement global “back button” system. You give a “paneable” target
to the application controller, the back button will modulate its
pane-related properties as necessary, and call an action when the
button is clicked.
- Extract welcome-hero into its own component.
- Lots of other general improvements/refactoring. The code is quite
well-commented so take a look!

ember/app/components/ui/controls/select-input.js

@@ -2,6 +2,8 @@ import Ember from 'ember';
 
 export default Ember.View.extend({
 	tagName: 'span',
-	classNames: ['select'],
-	layout: Ember.Handlebars.compile('{{view "select" content=view.content optionValuePath=view.optionValuePath optionLabelPath=view.optionLabelPath value=view.value}} {{fa-icon "sort"}}')
+	classNames: ['select-input'],
+	optionValuePath: 'content',
+	optionLabelPath: 'content',
+	layout: Ember.Handlebars.compile('{{view "select" content=view.content optionValuePath=view.optionValuePath optionLabelPath=view.optionLabelPath value=view.value class="form-control"}} {{fa-icon "sort"}}')
 });