v0.12.1

Minor release with lots of improvements after analysis with Sonarcloud.

• Google Java Style Guide is now enforced as part of the build.
• JaCoCo coverage is enforced as part of the the build - we're striving for 80%+ line coverage where possible. Notable exceptions are the exchange adapters and repositories classes - there is no way to use PowerMock with JaCoCo on-the-fly instrumentation. These classes are excluded from the metrics despite them being extensively tested.
• Sonarcloud report is generated as part of the CI build.
• The Cryptopia exchange adapter has been removed in light of recent events.

The REST API is still not production ready, but is being actively developed on the bxbot-restapi branch.