Introduce the Both[T] class
Use Both in CommitmentNotification
Use Both[T] for Deposits
Introduce MockMicroPaymentChannel
Fix timer cancellation

 * Make AkkaSpec and BitcoinjTest afterAll methods compatible to allow
   timer cancellation
 * Remove some dead code related with timers

This change fixes #189
Replace ProtoMicroPaymentChannel in BuyerMicroPaymentChannelActor
Merge pull request #205 from sortega/issues/41

Last preparations for replacing ProtoMicroPaymentChannel with MicroPaymentChannel
Add interface for PeerActor
Add replace BlockchainActor with PeerActor in ExchangeActor
Add last offer querying to MicropaymentChannel actors
Add ExchangeTransactionBroadcastActor interface
Add scaladoc to exchange actor
Add height notification capability to blockchain actor
Add constant value actor
Implement ExchangeTransactionBroadcastActor
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