Correct inconsistent generic typing in PushClient interface.
Fix Faye event parse bug.
Add error handling to the push client.

Don't try to reconnect when it's not ment to be so and also don't retry
to disconnect gracefully when already failed once.
Clean up domain objects.
Add dedicated callback interface for delivering events.

The SDK global ResultListener<T> callback interface didn't feel
very natural to use here as it inderectly implies an active user
initiated request (especially when reading out the callback method:
"onRequestPerformed". Push notifications doesn't seem like something
one would "request" - on the contrary, they are like sweet christmas
surprises. Hence, introducing the EventListener interface.