Bug 29434: add UNIMARC relationship codes for authorities

Bug 29434: add UNIMARC relationship codes for authorities

When using the authority finder plugin (authorities/auth_finder.pl),
you can pick an entry from the 'Special relationship:' dropdown menu
in order to set the relationship between authorities.

However, in UNIMARC instances the relationship codes listed are those
for MARC21. The correct codes for UNIMARC are listed in pages 93-94
of the IFLA UNIMARC Manual for Authorities.

Test plan:

1) In a UNIMARC instance, launch authorities/auth_finder.pl in the
   Staff client, by clicking on the 'Tag editor' button. Notice how
   the 'Special relationship:' dropdown menu lists the relationship
   codes for MARC21 instead of UNIMARC.
2) Apply this patch.
3) Launch the authority finder again; this time the correct values
   should be listed in the 'Special relationship:' dropdown menu.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>