all bank details can be updated from the payment module. Invoice
module now checks if the current user is in admin's "backup"
group before creating a backup. Invoice module also checks if a
surcharge should be added, or if pre-order is being used before
showing in ui. Manager module looks up buyer groups for all users
so that new purchases can be added with the correct price.
Payment module now has a callback action for editing bank details.
Purchase module looks up buyer groups for all users so that
purchases can be added with the correct price.