CMOR-tables: added few yet missing variables; Readme: updated with information about CV changes and variable mapping

- PalMod2 MIPtables based on CMIP6 MIPtables
- Read_CMORvars_xlsx_csv_json.py to create sqlite database out of the MIPtables
- CMORizing scripts and tables as created by https://c6dreq.dkrz.de
- SQL scripts to create and alter the sqlite database
- Version_Mapping_DB.py to create change history between versions of the miptables / data request
- Map_Between_Projects.py to move mapping information from CMIP6 to the PalMod2 mapping tables