Bug 20799: Add link from biblio to ILL detail view

Bug 20799: Add link from biblio to ILL detail view

Some ILL systems (e.g. Libris in Sweden) require a link between
a biblio and an ILL request. When such a link exists it is nice
to display an actual link from the biblio detail view to the
ILL request detail view. This patch adds such a link. For users
without ILL privileges, the requests should still show, but not
be clickable links.

To test:
- Make sure you have a couple of ILL requests created with the
  FreeForm backend. (FreeForm does not let you tie a request to
  a biblio through the UI, but we will add connections directly
  in the database.) Lets assume these have illrequest_id's a and b.
- Make sure you have a record, let's call the biblionumber x.
- Apply the patch and make sure there are no changes in the biblio
  detail view of biblionumber x.
- Log into the database and connect the biblio to the first request:
  UPDATE illrequests SET biblio_id = x where illrequest_id = a;
- Check that the biblio detail view now says this:
  "ILL requests: Request a"
- Verify that the "Request a" part is a working link to the detail
  view of ILL request a.
- Do this in the database:
  UPDATE illrequests SET biblio_id = x where illrequest_id = b;
- Check that the biblio detail view now says this:
  "ILL requests: Request a, Request b"
- Verify the links work as expected.
- Log in as a staff user and check that the requests are still
  listed, but not displayed as clickable links.
- Sign off

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>