New event delivery solution using RabbitMQ

Note that this is not pull request. But I would like to share those patches.
Also I would like to share a document. Motivation and feature details in here.

https://docs.google.com/presentation/d/1ET1yoxt8SyUmTF11Rl8sXpoqhH5k8BKnZ7eY3d01DDs/edit?usp=sharing

 Please enjoy and review it!