SubscriptionManager.IdentitiesSubscription: Draft adaption of
notifySubscriberByFCP() to *SynchronizationNotification

- instanceof won't work on specific type parameters of generics, we need
to use <?>. Thus, the assert is added which validates whether the
Notification is of the correct type.
- The FIXMEs are where the FCPInterface will have to be called once we
there implement API for this.
- Notice: We need to first check whether it is an End*Notification, we
must NOT first check whether it is a Begin*Notification: End* is a
subclass of Begin*.