Update Akka from 2.2.4 to 2.3.0

[ngocdaothanh]

Akka 2.3.0 released:
https://groups.google.com/forum/#!topic/akka-user/YMSlVTcxTKo
http://doc.akka.io/docs/akka/2.3.0/project/migration-guide-2.2.x-2.3.x.html

• Remove data handover for now (see Replace handover in Akka 2.2.x with persistence in Akka 2.3.x+ #6)
• auto-down is replaced with auto-down-unreachable-after

akka {
    actor {
      provider = "akka.cluster.ClusterActorRefProvider"
    }

    # This node
    remote {
      log-remote-lifecycle-events = off
      netty.tcp {
        hostname = "127.0.0.1"
        port = 2551  # 0 means random port
      }
    }

    cluster {
      seed-nodes = [
        "akka.tcp://[email protected]:2551",
        "akka.tcp://[email protected]:2552"]

      auto-down-unreachable-after = 10s
    }
  }