Merge pull request #433 from apoloval/port/432

[PORT] Fix cancel order button not disabled when pressed #432
Make `ConfigProvider` deal with missing peer ID in config
Stop considering peer ID optional in `MessageGatewaySettings`
Merge pull request #434 from apoloval/task/config-autogen

Make config provider deal with missing peer ID
Reduce AskPattern timeout error verbosity

And add its missing unit test
Bump to SBT 0.13.7

This provide faster SBT reload times and warnings on dependency
 evictions.
Downgrade scalatest

To avoid conflict with the scalatest version required by Akka testkit
Merge pull request #437 from sortega/less_verbose

Reduce AskPattern timeout error verbosity
Merge pull request #438 from sortega/bump_sbt

Bump sbt
Deep refactor of `model.Exchange`

The way `model.Exchange` was implemented was a little mess. This change moves
from a `model.Exchange` class with a generic state parameter into a hierarchy
of classes, each one representing a concrete exchange state.
Merge pull request #436 from apoloval/task/cf-174

Deep refactor of `model.Exchange`
Bug fix: Wallet actor was not restoring properly.
Merge pull request #439 from gotoalberto/master-server

[PORT] Bug fix: Wallet actor was not restoring properly.
Improve logging

Use scala-logging as logging front-end on all modules. Also, rearrange
dependencies to make most modules require just the logging front-end but
not the backend.

The final configuration is:

 * scala-logging: logging front-end for regular classes that delegates
on slf4j
 * akka-logging: logging front-end for actors, it also delegates on slf4j
 * slf4j: logging collector, all goes to logback
 * logbook: writes the actual log files
Make headless module be aggregated into root module
Fix bug introduced when improving the exchange model
Merge pull request #441 from sortega/fix_logging

Fix logging and a compilation problem in headless