Merge pull request #114 from sortega/feature/simplify_cake

Simplify cake pattern by using initialization messages
Refactor BrokerActor

Make BrokerActor
 
 * Use an initialization message
 * Extract timeout managing logic to ExpirationSchedule class
 * Move magic number to ProtocolConstants
 * Make traded currencies a configurable value
Use GatewayProbe on BrokerActorTest