Order fulfillment module

[MrBartusek]

One of the big missing features in stocked up is order fulfillment. Users should be able to create and update orders that are sent to customers.

There should be a couple of new entitites

• Customers - Customer name, e-mail address, shipping address, remarks
• Order - Order id (autogenerated), date, billing address, status, list of items. With reference to customer

Orders should probably include references to inventory items with names. They should not be cascade deleted with them, rather, the front should show something like "item does not exist anymore".