Replace RethinkDB message bus with RabbitMQ for pipeline execution

[yamalight]

Additional message bus is redundant

[yamalight]

basic implementation is pushed to this branch: https://github.com/Exynize/exynize-rest/tree/feature/one-messagebus
current issue is with absence of subscriber for id + '.out' messages that are supposed to be delivered to front-end.
possible solution - create non-persistent rabbit queues?

[yamalight]

Should be much easier using microwork. Needs to be done.