Fix covariant and contravariant type class method names

Signed-off-by: Galder Zamarreño <galder@zamarreno.com>
Make src/main/scala compile

* Generated test classes fail to compile, don't know why yet.
* Added maven scala plugin so that scala code is compiled.

Signed-off-by: Galder Zamarreño <galder@zamarreno.com>
Remove java generated test classes

Signed-off-by: Galder Zamarreño <galder@zamarreno.com>
Generated scala test classes compile now

* Add a maven clean step to remove generated src/main and src/test
scala classes.

Signed-off-by: Galder Zamarreño <galder@zamarreno.com>