Bug 20310: Introduce Koha::Biblio->host_record

Bug 20310: Introduce Koha::Biblio->host_record

This is a more generic method that allows you to get to the host record
as defined in MARC21 field 773$w. This control number is looked up in the
search engine (MARC21 field 001).

Note: The current implementation is based on MARC21 and does not change
behavior for UNIMARC.
This includes the follow-up originally submitted separately on Bugzilla,
dealing with multiple 773 fields.

Test plan:
Run t/db_dependent/Koha/Biblio/host_record.t

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