Introduce DefaultTcpPortAllocator

To help allocating TCP ports for integrated tests avoiding tests
stepping on each other when opening server sockets.  Remove
superseded NetworkTestUtils.
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