LP1187016 Prevent new copies on activated POs

If a PO has already been activated, prevent users from adding new copies
in the Item Count entry under the full lineitem copy grid.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Ben Shum <bshum@biblio.org>