show EPC QR code for easier payments

[Delapro]

This is a feature request.

When showing the xml file it would be great for simple invoices to show a qr code for SEPA payments, for example:

Further information: https://de.wikipedia.org/wiki/EPC-QR-Code.

This could be done with a library like this: https://github.com/neocotic/qrious.