Add scynapse-akka module

`scynapse-akka` implements an Axon event bus to Akka bridge as Akka extension.
I was looking at Akka ZeroMQ extension as an example when I began implementing this. https://github.com/akka/akka/blob/v2.3.6/akka-zeromq/src/main/scala/akka/zeromq/ZeroMQExtension.scala