Merge pull request #237 from sortega/issue/39_serial_ex

Extract DelegatedOrderFunds from OrderActor
Fix coinffeine-broker by providing missing setting
Merge pull request #238 from sortega/fix_server

Fix coinffeine-broker by providing missing setting
Simplify micropayment channel actor initialization
Rename ExchangeProgress to ExchangeUpdate

Rename Collaborators.resultListener to listener as it sends progress
updates and not only the final result.
Model exchange failure modes

Introduce aborting, successful and failed states
Use failed exchanges instead of bare exceptions

Now that the exchange models failures, use them instead of unstructured
exceptions.
Merge pull request #239 from sortega/issue/39_serial_ex

Model exchange failure modes