Changed the sorting to descending for sales and purchase lists

New feature: Document sorting

this feature can be activated in the "acadon upcoming features" page

if this feature is activated the following pages are sorted based on the document date:

Sales:

1. Sales Quotes
2. Sales Orders
3. Sales Return Orders
4. Sales Invoices
5. Sales Creditmemo's
6. Sales Blanket Orders
7. Sales list
8. Sales Last Invoice
9. Sales Last Quote/Order

Purchase:

1. Purchase Quotes
2. Purchase Orders
3. Purchase Return Orders
4. Purchase Invoices
5. Purchase Creditmemo's
6. Purchase Blanket Orders
7. Purchase List