Bug 22789: Add non priority feature to C4 classes and staff interface

Bug 22789: Add non priority feature to C4 classes and staff interface

This patch implements necesary code to implement non priority feature

To test:
1) Apply all patches.
2) Run updatedatabase.
3) Checkout a specific item for patron1.
4) Place a hold on the same item for patron2 (do not check non priority
   hold checkbox).
5) Try to renew the item for patron1.
CHECK => in checkouts table, there is a message that the item could not
be renewed because there was a hold.
6) Cleanup all checkouts and holds.
7) repeat steps 3 to 5, but this time check the non priority checkbox.
SUCCESS => item was renewed
8) prove t/db_dependent/Holds.t

Signed-off-by: Lisette Scheer <lisettes@latahlibrary.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>