Render group members in the message detail view

This requires that we fetch contact info when opening a conversation
so that's available for rendering contact names and avatars.

js/models/messages.js

@@ -40,6 +40,9 @@
         },
         isGroupUpdate: function() {
             return !!(this.get('group_update'));
+        },
+        isIncoming: function() {
+            return this.get('type') === 'incoming';
         }
     });