Add total VAT as part of Invoice

[fili]

As the following properties are part of Invoice:

• minimumPaymentDue
• totalPaymentDue

I would also expect the following properties to be added to Invoice:

• vatReverseCharged (Boolean)
• totalValueAddedTaxDue (MonetaryAmount or PriceSpecification)

vatReverseCharged is an important aspect on an invoice level (not item level) and depends on valid VAT numbers from Organization vatID. VAT still very much applies in these cases, hence we do want to add VAT and not pretend it is not included by using valueAddedTaxIncluded = False, but the responsibility who pays the VAT is moved from one organization (seller) to the other (buyer) and we need to add "VAT reverse-charged" to the invoice.

Here are a few links to the importance of VAT reverse charge:

• https://ec.europa.eu/taxation_customs/business/vat/eu-vat-rules-topic/vat-invoicing-rules_en
• https://www.belastingdienst.nl/wps/wcm/connect/bldcontenten/belastingdienst/business/vat/vat_in_the_netherlands/calculating_vat/reverse-charging_vat
• https://www.revenue.ie/en/vat/what-is-vat/what-is-reverse-charge-and-self-accounting.aspx
• https://www.gov.uk/guidance/the-vat-domestic-reverse-charge-procedure-notice-735 (not sure how long it will matter for the UK with Brexit)

[github-actions[bot]]

This issue is being tagged as Stale due to inactivity.