Merge pull request #325 from sortega/persistent_seller_channel

Make seller channel actor persistent
Remove unused stuff in CoinffeineClientTest
Refactor DefaultExchangeActorTest to use stubs
Avoid hostname resolution exception in static context
Catch start failures in main program

If the app fails to start, now it is reported with a dialog instead of letting
the exception to terminate the app.
Extract base class for testing the exchange actor
Rename ExchangeResult to ChannelResult

This avoids confusion with the ExchangeResult defined for the
ExchangeActor.
Merge pull request #326 from apoloval/task/cf-121

Fix abrupt app closing when broker is unreachable
Make exchange actor persistent

To do so, unlock funds just when the exchange finishes and not in
every postStop.
Remove prints from tests
Avoid a race condition on handshake actor tests

When stopping the handshake actor for testing how persistence recovers
its state we cannot reuse the actor name as there is a possibility of
trying to create the new actor when the old one has sent the Terminated
message but its actor queue is not yet removed from the actor system.
Make roles serializable
Fix broken equality of PeerInfo
Make CoinffeineUnitTestNetwork serializable
Introduce PersistentEvent marker trait
Introduce Kryo serialization for Akka

Include a custom serialized for KeyPair
Merge pull request #327 from sortega/issue/113_persistent_exchange

Make the exchange actor persistent