Qt Organizer: do not emit unnecessary collectionsChanged signals

Prevent emitting of unnecessary collectionsChanged signals
without collections modifications. These signals lead
to a reset without real changes of collections models
based on QList.

Change-Id: I7d36209e40c62a2c7d43340e645b3567754470b3
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>