Move error messages to message detail view

Change how message errors are rendered. Errors associated with a number
will be shown under that number in the detail view rather than piling up
in the message bubble.

// FREEBIE

js/models/messages.js

@@ -58,6 +58,9 @@
             if (this.isIncoming() && this.hasKeyConflicts()) {
                 return 'Received message with unknown identity key.';
             }
+            if (this.isIncoming() && this.hasErrors()) {
+                return 'Error decrypting incoming message.';
+            }
 
             return this.get('body');
         },
@@ -111,6 +114,9 @@
         isOutgoing: function() {
             return this.get('type') === 'outgoing';
         },
+        hasErrors: function() {
+            return _.size(this.get('errors')) > 0;
+        },
         hasKeyConflicts: function() {
             return _.any(this.get('errors'), function(e) {
                 return (e.name === 'IncomingIdentityKeyError' ||