LP#1440114 Blanket order PO "finalize"

LP#1440114 Blanket order PO "finalize"

When invoicing a PO that has at least one blanket charge, a new option is
present which allows staff to indicate that an invoice is the final invoice
for the PO.  Finalizing a PO results in the following:

1. Encumbrances for all blanket charges on the PO are dropped to $0.
   This is done by setting the amount paid in the original fund_debit
   (linked the blanket po_item) to $0.

2. If no pending lineitems exist on the PO, the PO is marked as received.
   If there are pending lineitems, the state is left untouched.

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