Fixes #718 - Remove the gateway ACK call 

Resurrected gateway unit tests!!

No ack gateway receiver backwards compatible with the old sender (proven with unit test)

Added simpler deduplication mechanism. Message body is no longer persisted.
Implementations
- in-memory
- RavenDB
- simple sql (no NHibernate)

New receiver manages databus property ids in memory only (databus properties arrive before the message body)

Haven't done any work on config. Happy for NSB devs to take over or provide guidance/help.