idviews: Handle Default Trust View properly in the framework
    
    Make sure that:
    1.) IPA users cannot be added to the Default Trust View
    2.) Default Trust View cannot be deleted or renamed
    
    Part of: https://fedorahosted.org/freeipa/ticket/3979
    
    Reviewed-By: Petr Viktorin <pviktori@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>