Autodetect system installation if cadet_path is not set

[schmoelder]

To simplify the use of CADET-Python, it would be helpful if a CADET installation could be automatically detected.
For an example implementation, see CADET-Process:
https://github.com/fau-advanced-separations/CADET-Process/blob/fa04e0d077b3fe186d631f1fe1fa202022a8b381/CADETProcess/simulation/cadetAdapter.py#L117

It is important to note that (at least for POSIX), environmental variables also need to be handled. See here:
https://github.com/fau-advanced-separations/CADET-Process/blob/fa04e0d077b3fe186d631f1fe1fa202022a8b381/CADETProcess/simulation/cadetAdapter.py#L146