Refactor implementation of Contracts java generator

[lhartl]

A concept for the Java generation of Contracts is needed in KernelF. Tests are failing. e.g.: iets3.os; branch feature/kernelf-tests http://127.0.0.1:63320/node?ref=r%3Aa2594bdc-f128-474d-863a-401664a7ab8e%28test.in.expr.os.todo%40tests%29%2F7981304192356751148&project=org.iets3.opensource and http://127.0.0.1:63320/node?ref=r%3Aa2594bdc-f128-474d-863a-401664a7ab8e%28test.in.expr.os.todo%40tests%29%2F867786408878183513&project=org.iets3.opensource