Faster invoicing and small fixes

Invoices open and send noticeably faster. A handful of small bugs in the product list and VAT setup are also fixed.

What is new

The invoice list and invoice view have been rewritten and now open noticeably faster, even with many lines. Sending happens in the background, so you can move on right away.

• The product list remembers your sorting
• VAT rates show correctly on credit notes
• The date field accepts periods and hyphens