const/strings for YAOUS: "forgive" lost billings

const/strings for YAOUS: "forgive" lost billings

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.

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