[API]: changed body mapping functions: removed most of them, added mapping-decider function, accomodated changes to test cases, added new mapping test case

[API]: changed pe coupling mapping functions interfaces, added new mapping functions, adapted test cases and benchmarks

If you have access to the old closed source waLBerla repository, you may restore the complete history with the following command
git fetch git@i10git.cs.fau.de:software/walberla.git 'refs/replace/*:refs/replace/*'