LP#1333254 Disencumber on invoice close

LP#1333254 Disencumber on invoice close

Set encumbrance=false on invoiced fund debits when the invoice is closed
(complete=true) instead of when the invoice is created.

To test:

1. Activate a purchase order.
2. Create an invoice for the PO.
3. Confirm PO shows same amount encumbered as befor invoicing and $0
   paid.
4. Close the invoice.
5. Confirm amount encumbered on the PO is reduced by the amount invoiced
   and the amount paid on the PO is increased by the amount invoiced.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>