Bug 32695: Fix search strings for 775, 780, 785 and 787

Bug 32695: Fix search strings for 775, 780, 785 and 787

In the past due to some misunderstanding of the MARC standard
we built the search links for these fields using $a and $t with
the title index. But we actually need to search $t as title
and $a as author.
This patch fixes the templates for the MARC 7xx fields:
* 775
* 780
* 785
* 787

To test:
* Ensure systme preference 'UseControlNumber' is set to don't
* Create a record with the linking fields above
* Look at the OPAC and staff interface detail views
* Verify the content of your fields shows and the links combine a+t as a title search
* Apply patch
* Verify you have nicely formatted links now

Example:
775 _ _ ‡asomeone‡ttitle775
780 0 2 ‡asomeone‡ttitle780
785 0 2 ‡asomeone‡ttitle785
787 _ _ ‡ilabel:‡ttitle787‡asomeone

Signed-off-by: Sabrina Kiehl <kiehl@mpis.mpg.de>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit b2b3d88b7335c542035fbdf11637fa2a31ea22bb)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>