Manual Merge branch 'toolkit2' of gitlab.lrz.de:exahype/ExaHyPE-Engine into toolkit2

Two changes I did and you unfortunately undid with your merge (should be easy to fix though): * Make sure you are using `ValueError` instead of `JSONDecodeError(ValueError)`. Otherwise, the code requires python3 version>=3.5.0. This is a typical error message you get: ``` controller.py:215(getSpec):ERROR Could not read specification file '../Euler_ADERDG.exahype': 'module' object has no attribute 'JSONDecodeError' ``` * Make sure `mexa.py` is python3. I regex-replaced `print (".+"\s*(%\s*\(.+\))?)$` with `print(\1)`