Render leave-group messages correctly

js/background.js

@@ -148,8 +148,8 @@
             var conversation = new Whisper.Conversation({id: conversationId});
             var attributes = {};
             conversation.fetch().always(function() {
-                if (pushMessageContent.group &&
-                    pushMessageContent.group.type === textsecure.protobuf.PushMessageContent.GroupContext.Type.UPDATE) {
+                if (pushMessageContent.group) {
+                    if (pushMessageContent.group.type === textsecure.protobuf.PushMessageContent.GroupContext.Type.UPDATE) {
                         attributes = {
                             type       : 'group',
                             groupId    : pushMessageContent.group.id,
@@ -162,6 +162,12 @@
                         if (difference.length > 0) {
                             group_update.joined = difference;
                         }
+                    }
+                    else if (pushMessageContent.group.type === textsecure.protobuf.PushMessageContent.GroupContext.Type.QUIT) {
+                        var group_update = { left: source };
+                        attributes = { members: _.without(conversation.get('members'), source) };
+                    }
+
                     if (_.keys(group_update).length > 0) {
                         message.set({group_update: group_update});
                     }

js/views/group_update_view.js

@@ -23,6 +23,11 @@
         className: "group-update",
         render: function() {
             //TODO l10n
+            if (this.model.left) {
+                this.$el.text(this.model.left + ' left the group');
+                return this;
+            }
+
             var messages = ['Updated the group.'];
             if (this.model.name) {
                 messages.push("Title is now '" + this.model.name + "'.");