[Bugfix - LOW] Prevent users from favoriting themselves

It should be noted that changing this should work on any new installation. However, what about the current installations which have users that have already favourited themselves? IMO, they should be removed by running a few update SQL queries in the next DB version. The downside of this is that no event will be fired but still I think is the right way to go as if events get fired and plugins get notified (if there exist any) maybe users won't understand what is going on.