LP#1380709 Fund debit links to invoice entry

LP#1380709 Fund debit links to invoice entry

Fund debits created by lineitem_details (copies) now track which invoice
entry last touched the fund debit.  With this, it's possible to say with
certainty which invoice a fund_debit "belongs" to, which is particularly
useful for reporting fund summary information on an invoice.

Note this has no affect fund_debit's linked to invoice_item's, since
they already link to the fund debits.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Jennifer Pringle <jennifer.pringle@bc.libraries.coop>