Add step number to StepSignature message
Add new function to Exchange trait
Add basic failure handling to BuyerExchangeActor
Merge pull request #175 from edrevo/implement-error-handling-in-exchange

Implement error handling in BuyerExchangeActor
Adapt PasswordStepPane to the style of other steps
Move BitcoinjTest to common
Merge pull request #176 from sortega/task/40_wizard_steps

Adapt PasswordStepPane to the style of other steps
Merge pull request #177 from sortega/task/41_abstract

Move BitcoinjTest to common
Add domain model for the exchange protocol
Move main window to a new package
Introduce the concept of application view
Introduce a view selector
Introduce CSS for the wizard
Move multisig deposit creation to TransactionProcessor
Minimize the impact of Transaction being mutable
Merge pull request #178 from sortega/task/41_abstract

Introduce untested domain model for the exchange protocol
Require at least one view in ApplicationScene
Merge pull request #179 from sortega/task/54_main_view

Introduce views and CSS into the UI
Turn `PaymentProcessor` into an actor

`PaymentProcessor` trait is aimed to be used in an asynchronous way by
producing `Future` objects. Since we already have Akka to deal with
async IO, it is convenient to consider the payment processors as
another actor.

This change turns `PaymentProcessor` trait into a hierarchy of
actors. The same functionality is implemented in a message-passing
approach.

This addresses [task 52](http://redmine.coinffeine.com/issues/52).
Add ExchangeSupervisorActor