LP1211473 YAOUS : disable patron credit payments

New org unit setting circ.disable_patron_credit.

This prevents "patron_credit" payments in the payment creation API and
hides all patron credit related actions in the patron payment interface.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Dan Wells <dbw2@calvin.edu>
Stamping 'patron credit disable' setting

Signed-off-by: Dan Wells <dbw2@calvin.edu>