+'ChangeTagsAllowedAdd': Called when checking if a user can add tags to a change.
+&$allowedTags: List of all the tags the user is allowed to add. Any tags the
+ user wants to add ($addTags) that are not in this array will cause it to fail.
+ You may add or remove tags to this array as required.
+$addTags: List of tags user intends to add.
+$user: User who is adding the tags.
+