Remove unregistered group members

Locally remove unregistered users from group membership lists.

Fixes #989
Related to Whispersystems/Signal-Android#6175
Closes #1052

// FREEBIE

js/models/conversations.js

@@ -62,6 +62,19 @@
         message.save().then(this.trigger.bind(this,'newmessage', message));
     },
 
+    addMemberLeft: function(source) {
+        var timestamp = Date.now();
+        var message = new Whisper.Message({
+            conversationId : this.id,
+            source         : source,
+            type           : 'incoming',
+            sent_at        : timestamp,
+            received_at    : timestamp,
+            group_update   : {left: source}
+        });
+        message.save().then(this.trigger.bind(this,'newmessage', message));
+    },
+
     onReadMessage: function(message) {
         if (this.messageCollection.get(message.id)) {
             this.messageCollection.get(message.id).fetch();

js/models/messages.js

@@ -201,21 +201,36 @@
                 this.sendSyncMessage();
             }.bind(this)).catch(function(result) {
                 var now = Date.now();
+                var errors;
+                var conversation = this.getConversation();
                 this.trigger('done');
                 if (result.dataMessage) {
                     this.set({dataMessage: result.dataMessage});
                 }
 
                 if (result instanceof Error) {
-                    this.saveErrors(result);
+                    errors = [result];
+                    this.saveErrors(errors);
                 } else {
-                    this.saveErrors(result.errors);
+                    errors = result.errors;
+                    this.saveErrors(errors);
                     if (result.successfulNumbers.length > 0) {
                         this.set({sent: true, expirationStartTimestamp: now});
                         this.sendSyncMessage();
                     }
                 }
 
+                if (conversation.get('type') === 'group') {
+                    errors.forEach(function(e) {
+                        if (e.name === 'UnregisteredUserError') {
+                            textsecure.storage.groups.removeNumber(conversation.id, e.number);
+                            conversation.addMemberLeft(e.number);
+                            conversation.set({
+                                members: _.without(conversation.get('members'), e.number)
+                            });
+                        }
+                    });
+                }
             }.bind(this));
         },