Bug 7267: Add account number to German PDF template

Bug 7267: Add account number to German PDF template

To test:
- Switch system preference OrderPdfFormat to pdfformat::layout2pagesde
- Create one or more baskets with some orders each.
- Add all baskets to one basket group
- Print the basket group
- Check the account number from your vendor shows up with the other
  vendor details

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>