Bug 27358: Add GET /public/biblios/:biblio_id/items

Bug 27358: Add GET /public/biblios/:biblio_id/items

This patch introduces a route to fetch items belonging to a biblio. It
is expected to return the 'public' representation of the Koha::Item
objects.

It is also enforcing the visibility rules, by using
Koha::Items->filter_by_visible_in_opac.

To test:
1. Apply this patches
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/biblios.t
=> SUCCESS: Test pass and they cover all the cases!
3. Try your favourite REST tool against the new route.
4. Sign off :-D

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>