Bug 20793: Don't show a holds link in staff for users without permission

Bug 20793: Don't show a holds link in staff for users without permission

On the results list in staff the 'Holds (x)' link always shows
independent of the permissions of the staff user.

This patch tightens the permission checks on the result page
to explicitly check for the place_holds permission.

To test:
- Create a staff user with place_holds permission
- Check the result list, you should see 2 links to the
  holds page:
  - 'Place holds' on top of the results list
  - 'Holds (x)' at the bottom of each entry in the results
     list
  - Verify both links work
- Create a staff user without place_holds_permission
  - Without the patch you'll see the second link,
    but it will lead to a permission error
  - With the patch you'll still see the 'Holds (x)', but
    it will no longer be a link.
- Go to the detail page of a record with an existing hold.
  - Repeat test with both staff users.
  - One time the Hold information in the bibliographic information
    should show as a link, the other time as a simple text.

Displaying the information about existing holds still make sense
as this is the current beheviour.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>