Fix up bug with the way we hide list items

If we use an #unless condition, then when the view is removed from the
template, it is destroyed, and cannot be inserted again. So we’ll just
keep the item there the whole time, and toggle its visibility with CSS.

ember/app/components/discussion/post-header/edited.js

@@ -9,8 +9,9 @@ var precompileTemplate = Ember.Handlebars.compile;
   hover which details who edited the post and when.
  */
 export default Ember.Component.extend({
-  tagName: 'span',
+  tagName: 'li',
   classNames: ['post-edited'],
+  classNameBindings: ['hidden'],
   attributeBindings: ['title'],
   layout: precompileTemplate('{{fa-icon "pencil"}}'),
 
@@ -20,7 +21,7 @@ export default Ember.Component.extend({
 
   // In the context of an item list, this item will be hidden if the post
   // hasn't been edited, or if it's been hidden.
-  hideItem: Ember.computed('post.isEdited', 'post.isHidden', function() {
+  hidden: Ember.computed('post.isEdited', 'post.isHidden', function() {
     return !this.get('post.isEdited') || this.get('post.isHidden');
   }),