Introduce PeerActor

Make QuoteTest fail because the peer doesn't process QuoteRequest
messages. Also, introduce some infrastructure for matching futures.
Move system package to coinffeine-common
Add parser of peer command line arguments
Introduce PeerSupervisorActor

To have a PeerActor and a ProtoRpcMessageGateway available on the
acceptance tests. Current failure on acceptance test QuoteTest:
cannot forward message QuoteRequest(EUR) to coinffeine://fake:4790/

This can be solved by having an actual broker on the acceptance tests.
Move GatewayProbe to a place to be reused