Bug 24592: Reword LOST_RETURN to LOST_FOUND

Bug 24592: Reword LOST_RETURN to LOST_FOUND

This patch updates the wording in the 'lost and found' process to more
closely reflect what the process is achieving by replacing 'RETURNED'
with 'FOUND'

Test plan:
1) Grep codebase for _FixAccountForLostAndReturned and note there are no
   longer any instanced of it.
2) Run t/db_dependent/Circulation.t and note it passes
3) Test returning/renewing an item that has been marked as lost and note
   the updated values in the accountlines now use LOST_FOUND as
   credit_type_code and 'FOUND' as the status for the 'LOST' fee
   (debit_type_code 'LOST')

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>