Rework mvs_parameters.csv to be consistent with constants.py

[SabineHaas]

• [ ] All default values in mvs_parameters.csv are given as None, but should be the same as in constants.py (?).
• [x] Column unit is used inconsistently: either give type or unit of parameter value.

[smartie2076]

This is more an issue of "None" being used as "NaN", but not as an actual value. There is currently nothing that checks the validity of input parameter values, and so the info from constants.py is applied, not the one from mvs_parameters.csv

[smartie2076]

Connected to #586

[smartie2076]

@Bachibouzouk did you close this as well with #586?

[Bachibouzouk]

Now with #956 the default are taken first from constants.KNOWN_EXTRA_PARAMETERS and otherwise from the docs/MVS_parameters_list.csv. I guess it would make sense to get rid of KNOWN_EXTRA_PARAMETERS and to fill REQUIRED_CSV_PARAMETERS from docs/MVS_parameters_list.csv by filtering with the column category one can know in which asset category the parameter is expected.