Account Payment Widget Amount

When you open a customer invoice or vendor bill that has outstanding credits or debits, the payment widget normally applies the whole outstanding amount. This module changes that: clicking the outstanding item now opens a small pop-up titled "Enter the payment amount" with a Paid Amount field pre-filled with the available amount and an Apply button.

• You type the amount you want to assign to the invoice and press Apply; only that amount is reconciled.
• The remaining part of the payment stays outstanding and can be applied later to another invoice.
• The amount is applied across the outstanding items in order, stopping once the amount you entered is used up.
• If the invoice and the payment are in different currencies, the entered amount is converted using the company currency and the relevant dates, so the reconciliation stays correct.

The change appears directly in the invoice form's payment widget; no new menu is added. It touches account.move and account.move.line, and works together with the standard outstanding credits/debits widget.