Add ExchangeSupervisorActor
Rename exchange-related actor classes
Merge pull request #181 from edrevo/add-exchange-supervisor

Add ExchangeSupervisorActor
Merge pull request #180 from apoloval/issues/52

Turn `PaymentProcessor` into an actor
Fix build break
Merge pull request #185 from edrevo/fix-build-break

Fix build break
Add test for handshake start

Also, fix issues to make it pass
Refine and test the exchange model

Refine and test the exchange model up to the handshake step
Add missing tests to DefaultHandshakeTest
Refactor Exchange.Amounts
PR feedback
Address some feedback from PR #184

* Rename `Exchange.startHandshake()` to `Exchange.createHandshake()`.
* In `DefaultHandshake`, introduce an additional validation of
refund transactions that checks the correctness of the refund amounts.
* Fix some typos in Scaladoc
Add failure handling for SellerExchangeActor
Ensure Akka test time factor also affects Scalatest
Addressed some feedback from PR #184

* In `DefaultHandshake`, move refund validation into function
`signRefundTransaction()`.
* In `DefaultHandshake`, remove fruitless confidence type checks.
* Make package private all members of `impl` package.
Merge pull request #182 from edrevo/implement-error-handling-in-exchange

Add failure handling for SellerExchangeActor
Merge pull request #186 from apoloval/issues/41

Refine and test exchange model (Cont.)