Implement Akka Cluster for Scalachain Cluster creation

[elleFlorio]

The introduction of Akka Cluster will enable and facilitate the discovery and communication between Scalachain nodes.

It is required to integrate Akka Cluster inside scalachain at a basic level:

• every node should register itself in the cluster
• the nodes should be able to start also in docker containers in the same machine

The implementation of cluster logics (cluster event handling, communication, etc.) will follow in later issues