Incompatible with python 3.13 since cgi was removed

[mscherer]

On https://github.com/wbond/vat_moss-python/blob/master/vat_moss/id.py#L7 and https://github.com/wbond/vat_moss-python/blob/master/vat_moss/exchange_rates.py#L5 , the code import cgi. This was removed in python 3.13, and so the mobule no longer work without installing the python package legacy-cgi.