Let messages fetch references to senders

The conversation's contactCollection only contains references to the
current membership, and will not provide contact info for people who
have left the group, causing their messages to render without numbers or
avatars.

// FREEBIE

js/models/messages.js

@@ -97,9 +97,16 @@
             return this.imageUrl;
         },
         getContact: function() {
-            if (this.collection) {
-                return this.collection.conversation.contactCollection.get(this.get('source'));
+            var conversationId = this.get('source');
+            if (!this.isIncoming()) {
+                conversationId = textsecure.storage.user.getNumber();
             }
+            var c = ConversationController.get(conversationId);
+            if (!c) {
+                c = ConversationController.create(conversationId);
+                c.fetch();
+            }
+            return c;
         },
         isOutgoing: function() {
             return this.get('type') === 'outgoing';