Pyproject.toml transition

Move building the package from setup.cfg to pyproject.toml. How it looks on PyPI can be viewed here:
https://test.pypi.org/project/plotID/
It remains to be discussed who we should mention as author in the init.py which is used for the author in the documentation. But I actually like that the author is the institute in the documentation but is referenced as last in the metadata...

Closes #89 (closed)