LP#1538691: Use items instead of copies

LP#1538691: Use items instead of copies

For better consistency for the terms used in the client, let's use items instead
of copies, which was the preference of most people who provided feedback on bug
1538691.

Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Conflicts:
        Open-ILS/src/templates/staff/cat/catalog/t_holds.tt2
        Open-ILS/src/templates/staff/cat/item/t_list.tt2
        Open-ILS/src/templates/staff/cat/item/t_summary_pane.tt2
        Open-ILS/src/templates/staff/circ/holds/t_shelf_list.tt2

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