Added UnhandledMessageForwarder, a UnhandledMessage.ToDebug() extension
and attached it to StartDefaultLoggers when DebugUnhandledMessages is
enabled via subscribing to the EventBus

UnhandledMessageForwarder now subscribes to the UnhandledMessage
added a test verifying that unhandled message debugging works.
Merge pull request #445 from mmisztal1980/i391

Unhandled messages should now be forwarded as Debug messages when DebugUnhandledMessages setting is enabled. Fixes #391