Hazelcast and Coherence: TX, querying...

This PR brings some refactoring and new features that are mostly targeted at Hazelcast and Coherence.
Regrettably, Coherence transactional support is not working yet - still, I'd prefer to have implementation in repo. Transactional support for Coherence is therefore disabled (commented out).
Oops, rollback() should be here, of course... And yes, this could be delegated through anonymous Runnable