Add total amount on dunning
Following https://discuss.tryton.org/t/reminder-procedure-and-partial-invoice-payment/3704/4 We could add a global total amount as all the dunning are in the past and so this total represent the due today.
Following https://discuss.tryton.org/t/reminder-procedure-and-partial-invoice-payment/3704/4 We could add a global total amount as all the dunning are in the past and so this total represent the due today.