Use component prototypes instead of instances

This means the component instance is created in the template, meaning
properties can be overridden in the view helper. It also just makes
more sense - a view instance doesn’t need to exist until it is rendered
in the template.

ember/app/components/composer/composer-reply.js

@@ -12,7 +12,7 @@ export default ComposerBody.extend({
   submitLabel: 'Post Reply',
 
   populateControls: function(items) {
-    var title = Ember.Component.create({
+    var title = Ember.Component.extend({
       tagName: 'h3',
       layout: precompileTemplate('Replying to <em>{{component.discussion.title}}</em>'),
       component: this