Do proper Activity-plugin based mention notification

plugins/Favorite/classes/Fave.php

@@ -324,6 +324,11 @@ class Fave extends Managed_DataObject
         return $object;
     }
 
+    public function getAttentionArray() {
+        // not all objects can/should carry attentions, so we don't require extending this
+        // the format should be an array with URIs to mentioned profiles
+        return array();
+    }
 
     public function getTarget()
     {