Bug 19550: Add links to related authorities for UNIMARC

Bug 19550: Add links to related authorities for UNIMARC

Links exist in search results for MARC21 but not for UNIMARC.
This patch fixes that.

Test plan:
1. Create an authority with a field 550 that links to another authority
   e.g. 550 $a Foo $9 42
2. Reindex this authority
3. Search for this authority
4. See that you now have a link "Foo" to authorities/detail.pl?authid=42
   in the summary

Signed-off-by: delaye <stephane.delaye@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>