Revised code of domain objects and added more tests
Changes to avoid conflicts when measuring code coverage with JaCoCo

JaCoCo adds a static private method $jacocoinit() which is added to
every non-interface class. This breaks the expected test result and
therefore we should analyze classes of another package or better of
another library.
Switched from Cobertura to JaCoCo to measure code coverage
Separated utility to generate some code from unit tests