Implement "renamed" posts

Record when the discussion was renamed, from what, and by whom.
Information is stored in the `content` field as a serialised JSON
object because proper polymorphism will be too difficult with Ember
Data and especially when extensions try to add new post types.

ember/app/components/discussion/post-renamed.js

@@ -0,0 +1,48 @@
+import Ember from 'ember';
+
+import FadeIn from 'flarum/mixins/fade-in';
+import HasItemLists from 'flarum/mixins/has-item-lists';
+
+var precompileTemplate = Ember.Handlebars.compile;
+
+/**
+  Component for a `renamed`-typed post.
+ */
+export default Ember.Component.extend(FadeIn, HasItemLists, {
+  layoutName: 'components/discussion/post-renamed',
+  tagName: 'article',
+  classNames: ['post', 'post-renamed', 'post-activity'],
+  itemLists: ['controls'],
+
+  // The stream-content component instansiates this component and sets the
+  // `content` property to the content of the item in the post-stream object.
+  // This happens to be our post model!
+  post: Ember.computed.alias('content'),
+
+  decodedContent: Ember.computed('post.content', function() {
+    return JSON.parse(this.get('post.content'));
+  }),
+  oldTitle: Ember.computed.alias('decodedContent.0'),
+  newTitle: Ember.computed.alias('decodedContent.1'),
+
+  populateControls: function(items) {
+    this.addActionItem(items, 'delete', 'Delete', 'times', 'post.canDelete');
+  },
+
+  actions: {
+    // In the template, we render the "controls" dropdown with the contents of
+    // the `renderControls` property. This way, when a post is initially
+    // rendered, it doesn't have to go to the trouble of rendering the
+    // controls right away, which speeds things up. When the dropdown button
+    // is clicked, this will fill in the actual controls.
+    renderControls: function() {
+      this.set('renderControls', this.get('controls'));
+    },
+
+    delete: function() {
+      var post = this.get('post');
+      post.destroyRecord();
+      this.sendAction('postRemoved', post);
+    }
+  }
+});