Bug 14371: Facets should be sorted by label (displayed) not title (link value)

Bug 14371: Facets should be sorted by label (displayed) not title (link value)

This patch changes one small line in catalogue/search.pl and opac/opac-search to sort facets by:
facet_label_value
instead of
facet_title_value

To test:
1 - Perform a search with results in two branches e.g. Centerville (code CPL) and Fairfield (code FPL)
2 - Notice that branch facets appear correctly sorted
3 - Rename the branches Centervile->Zebra and Fairfeild->Aardvark (but don't change codes)
4 - Repeat original search
5 - Note that branch facets are no longer correctly sorted
6 - Apply patch
7 - Repeat search
8 - Facets should be correctly sorted
9 - Test in both staff and opac search
10 - Ensure there are no unintended consequences/regressions

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Work as described,  staff AND opac
No errors

Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>
(cherry picked from commit 219f7b5c8fe59034fc7aff1ab81e42bc8cb6eba2)
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>