Fix usage of user.has_perm with object permissions

When using user.has_perm() with an object as argument, the permission must have the same origin as the related model. Otherwise, Django throws an exception.

But request.user.has_perm("alsijil.view_assigned_grouproles", register_object) makes use of a permission from Alsijil and a model from Chronos (LessonPeriod, Event, ExtraLesson).