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).
Yes, dumb user can set transactionSize="-1" in benchmark configuration, and we should handle that - checking transactionSize <= 0 is 'safer' than just transactionSize == 0.