Rename "handle()" event-handler functions to have a suffix:
- This will make classes which implement many of them easier to read.
Rename public event-handlers to something which I like better
Get rid of specific sub-interfaces of SubscriptionSynchronizationHandler<T> / SubscribedObjectChangedHandler<T>:
- This allows implementing classes to keep their implementation generic. This applies especially to DebugFCPClient.