Support forgive-vs void on Lost/Lost-checkin

Support forgive-vs void on Lost/Lost-checkin

Constants and strings for new OU settings:

circ.forgive_overdue_on_lost
circ.forgive_lost_on_checkin
circ.forgive_lost_proc_fee_on_checkin

These are intended for use as an alternative to their "void"
counterparts in situations where the library does not refund
fees and fines, and wishes funds taken in for one purpose or
billing type to not be re-applied toward a different billing
type as a result of voiding bills after they have been paid.

When circ.forgive_overdue_on_lost is set, attempt to make a
payment of type "Forgive" on the transaction for the amount
of outstanding overdue billings.

Only outstanding bills of type 1 (Overdue materials) will
be paid, and only the first contiguous grouping. If the
system finds an outstanding billing of type other than 1,
it will pay what it has found up to that point.

circ.forgive_overdue_on_lost has priority over the "void"
version of the same setting, if both happen to be set.

When circ.forgive_lost_on_checkin and/or
circ.forgive_lost_proc_fee_on_checkin is set, make a Forgive payment
on outstanding Lost and Lost Processing Fee bills on checkin of a
lost item.

New utility function:

outstanding_bills_for_circ (in AppUtils) accepts an editor and a
circ object, and will return a reference to an array of outstanding
billing objects. this has been broken out of the forgive_overdues
sub, as it will be useful elsewhere.

Signed-off-by: Jeff Godin <jgodin@tadl.org>