extract PO name from picklist upload

If a PO name is encoded in a lineitem (via provider attribute
definition), extract that PO name when creating a new purchase order
from lineitems that were previously only linked to a selection list.
This allows staff to create selection lists first, then orders second,
while retaining the encoded purchase order name.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>