Merge pull request #191 from sortega/issues/41

Implement DefaultMicroPaymentChannel
Use ExchangeId everywhere

Rename Exchange.Id to ExchangeId and move it to the messages package
and then use it whenever an exchange should be identified.
Use Exchange.Parameters from ExchangeInfo
Use Exchange.BrokerInfo in ExchangeInfo
Remove unneeded genericity from PeerInfo class
Use Exchange.PeerInfo in ExchangeInfo
Use a complete Exchange and a Role in ExchangeInfo