Bugfix #28: ClassCastException if configuration is provided

scala.util.parsing.JSON.parseRaw() returns an Option[JSONType] - None if
it could not decode it or Some(x) if it could. x may also be of another
type (like JSONArray), so the code now throws a DecodeException if it
wasn't decodeable.
Organized imports
Fix #28: Add tests to verify Vert.x/Scala JSON conversion works
Small tweak to lazily evaluate the message if log level is enabled.