Account voucher display writeoff

Display writeoff options on sale or purchase vouchers. Without setting these options explicitely, if a payment difference is encountered on vouchers of these types, it is booked on the account payable or account receivable which can pose problems for automatic reconciliation.

This addon also enables setting the voucher type as a selection criterium for default values, so that you can set different default values for writeoff settings for different voucher types.

At Therp, we use this functionality to write off small rounding differences when applying an inclusive tax on purchase vouchers. This is currently depending on lp:827649 for which we are proposing a fix.