pandas not listed as required dependency

[arthur-e]

I was dismayed to discover, after a long-running sampling, that pandas is a required dependency for spotpy.analyser.plot_parameterInteraction(). This should be listed in the setup.cfg or setup.py files so that it is installed when spotpy is installed.

Traceback (most recent call last):
...
  File "/home/arthur.endsley/python-env/smap-l4c/lib/python3.7/site-packages/spotpy/analyser.py", line 939, in plot_parameterInteraction
    import pandas as pd
ModuleNotFoundError: No module named 'pandas'

[thouska]

Added as proposed