Refactor inputs for Grassim

Summary

Some inputs parameters/files are not in appropiate file/folder

Current behaviour

Many inputs parameters should change their place for more user-convenience and consistency of the model

• Soil parameters in Parameters_values_PFT : Tref;K;percentageofNmin;NH3volatfactor
• Soil parameters directly in the run_grassim.py script : FNAmax, NSc
• dead biomass N content (plant.py, line 73) should be a parameter
• Useless files in INPUTS to move or delete for clarity : Kc_values (in duplicate), PFT_composition_example.yaml (empty file), WEATHER_Gembloux_2016.csv (not its place), Management.yaml (incomplete and not its place but fertilizer parameters to keep in management_dates_example.yaml), crop_init_Gembloux (move to subfolder 'crop')

Desired behaviour

• the soil parameters from PFT -> soil_init.yaml
  NB : hydraulic_properties remain in the same csv
• dead biomass N content -> parameters_values_PFT.csv
• FNAmax, NSc -> soil_init.yaml

Could also be interestinf to create a yaml file with the methods wanted for some formalisms instaed of defining them in the run_grassim.py but not for now to avoid too many parameters.