Upgrade to Ember 1.11-beta.1

HTMLBars goodness! Since there was some breakage and a lot of fiddling
around to get some things working, I took this opportunity to do a big
cleanup of the whole Ember app. I accidentally worked on some new
features too :3

Note that the app is still broken right now, pending on
https://github.com/emberjs/ember.js/issues/10401

Cleanup:
- Restructuring of components
- Consolidation of some stuff into mixins, cleanup of some APIs that
will be public
- Change all instances of .property() / .observes() / .on() to
Ember.computed() / Ember.observer() / Ember.on() respectively (I think
it is more readable)
- More comments
- Start conforming to a code style (2 spaces for indentation)

New features:
- Post hiding/restoring
- Mark individual discussions as read by clicking
- Clicking on a read discussion jumps to the end
- Mark all discussions as read
- Progressively mark the discussion as read as the page is scrolled
- Unordered list post formatting
- Post permalink popup

Demo once that Ember regression is fixed!

ember/app/components/index/welcome-hero.js

@@ -0,0 +1,19 @@
+import Ember from 'ember';
+
+/**
+  Component for the "welcome to this forum" hero on the discussions index.
+ */
+export default Ember.Component.extend({
+  layoutName: 'components/index/welcome-hero',
+  tagName: 'header',
+  classNames: ['hero', 'welcome-hero'],
+
+  title: '',
+  description: '',
+
+  actions: {
+    close: function() {
+      this.$().slideUp();
+    }
+  }
+});