Processing - addition of duplicate_columns

For later: a duplicate_columns would be nice, as processs ApplyExpression automatically replaces the selected columns. 
Or a modification in ApplyExpression.
For instance, 

`"new_unit": {
        "J": [["ApplyExpression", ["X / 3.6e+6", "kWh", "False"]]],` with False for inplace=False.

Both J and kWh are kept