Bug 16074: Making frequencies actions buttons

 Bug 16074: Making frequencies actions buttons

To test:

1) Go to Serials -> Manage frequencies
2) Confirm that buttons 'Modify' and 'Delete' show as buttons and work
   as expected
3) Confirm that when you make your window narrow, the column with the
   buttons does not wrap
4) Confirm that column heading is now 'Actions'

Sponsored-by: Catalyst IT
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Buttons look correct and work correctly.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>