FCPInterface.sendChangeNotification(): Adapt to fred plugin-fcp-rewrite

Use the new sendSynchronous(). It...
- Throws IOException instead of the existing Exceptions.
- Additionally throws InterruptedException in case of timeout
- Returns the reply, which might tell that the client failed to process
the notification. In that case, we also throw, so SubscriptionManager
can re-send the notification for a certain amount of retries