#3159 - ReliableProxy with reconnection

ReliableProxy with reconnection.  Fixes #3159

  * When the proxy receives Terminated for the tunnel it goes into a Reconnect state which uses Identify/ActorIdentity to resolve a new ActorRef.
  * Adds new constructor parameters reconnectAfter and maxReconnectAttempts (see Scaladoc).
  * Adds new messages ProxyTerminated, Unsent and NoRetry (See Scaladoc).
  * TODO: additional unit tests for new behavior.