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/routes/index/index.js

@@ -0,0 +1,13 @@
+import Ember from 'ember';
+
+export default Ember.Route.extend({
+
+	// When we enter the discussions list view, we no longer want the
+	// discussions list to be in pane mode.
+    setupController: function(controller, model) {
+        this.controllerFor('index').set('paned', false);
+        this.controllerFor('index').set('paneShowing', false);
+        this._super(controller, model);
+    }
+
+});