DebugFCPClient: Implement EndSubscriptionSynchronizationHandlerImpl
DebugFCPClient.SubscribedObjectChangedHandlerImpl: Store generic class

- Due to the way Java is implemented, it wouldn't be possible to obtain
this at runtime.
- Will be needed for the following commit.
DebugFCPClient.*.handleSubscribedObjectChanged(): Adapt to new sync
mechanism