Add support for post-Brexit VAT numbers with latest python-stdnum version
Remove use of country_id.intrastat
Add 'vat' field on computation and declaration lines with a simple validity check
Add 'partner_id' field on computation lines
Prevent back to draft when an XML export is present
Remove the universal constaint applied to the hs_codes for countries in the "Europe" list, as discussed in https://github.com/OCA/intrastat-extrastat/pull/116#discussion_r569735555
Co-authored-by: Alexis de Lattre <alexis.delattre@akretion.com>
