Allowing specification of referenced object id

Notifications for liked objects suffer from the objectID column referencing the likeID, but this creates a situation where identifying notifications for a certain object (e.g. a post) require an additional roundtrip.

The baseObjectID is used nowhere within the notification system, you can store anything you want and still be able to programmatically retrieve notifications based on it.
Merge branch 'master' of github.com:WoltLab/WCF