Bug 31421: Add a limited option to template plugin

Bug 31421: Add a limited option to template plugin

This adds a specific 'limited' routine to the Categories plugin, and uses
it for the new patron dropdowns

To test:
1 - Limit a patron category to some branches
2 - Sign in not at one of those
3 - Confirm the new patron dropdowns don't include the category

Bug 31421: (follow-up) Add POD

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>