Bug 32264: Fix capitalization and terminology: Show in Staff client?

Bug 32264: Fix capitalization and terminology: Show in Staff client?

This fixes several occurences of Staff client to read
staff interface.

To test:
* Activate the search filter feature via the SavedSearchFilters
  system preference
* Do a search in the staff catalogue
* Use the link "save as search filter" on top of the results list
* Verify it reads "Show in Staff client?" in the form
* Go to administration > search filters
* Verify the table has a heading "staff client"
* Edit the filter
* Verify there is the "Show in staff client" again
* Apply patch
* All those spots should now read 'staff interface'

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>