LP1878079 Staffcat Add Holdings action support

LP1878079 Staffcat Add Holdings action support

Teaches the staff catalog Add Holdings button to open the holdings
editor using the appropriate parameters.  If the holdings maintenance
grid is active, arguments to pass are based on the grid selection.
Otherwise it simply open the item editor with a single call number /
copy to be created 'here'.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>