Add payment due and paid/not paid on expenses

[flummer]

To help the handling of expenses, it would be nice to change or add a few things on the expense, so that it's clearer what state the expense is in, what has happened with the payment and what needs to be done.

If could eg. be

• a new field with a payment due date and a flag that specifies if it has been paid or not
• and/or maybe a choicefields, having options like: "paid by me, reimbursement needed", "paid by BornHack in netbank", "Should be paid by BornHack in netbank", "paid with BornHack mastercard", "paid with cash from infodesk", etc.

A "paid" flag could be used to make a backoffice list under Economy of expenses that needs to be paid in the bank, where it is not a reimbursement to a user (usually where BornHack have a line of credit with the supplier to speed up delivery)

[tykling]

WIP

• payment method choicefield:
• • paid with bornhack mastercard
• • needs reimbursement
• • unpaid invoice