Exclude user.notifications changes from creating a user revision

[benfurber]

Right now, there's no exemptions from when backupUser will create a revision from a change to a user. This creates a bunch of mostly useless revisions whenever a new notification is added (or all are removed) to user notifications.

Let's add a WELL TESTED exception in backupUser that doesn't create a new revision if the only change is in user.notifications