generate.groovy: remove trailing whitespace
generate.groovy: clean up style
Do not hardcode generated package prefix

It is more flexible to define each template's directory based on its
location beneath the templates directory itself, and allow the groovy
script take care of creating the right directories.
POM: add generated tests to the test sources, too

We want to autogenerate not only OPS classes, but also their tests.
This change puts them in the analogous location to the main sources:

   target/generated-test-sources/from-templates/