Bug 30036: Allow XSLT for authority results view in OPAC

Bug 30036: Allow XSLT for authority results view in OPAC

This patch adds a syspref to allow customizing the authority results
view at OPAC with XSLT

Test plan:
1. For testing make sure to have at least one or more authorities
   defined
2. OPAC: Home > Authority search(Submit) > Authority search results
   Notice the normal view of results
3. Apply patch
4. INTRA: Home > Administration > System preferences ->find
   "AuthorityXSLTOpacResultsDisplay"
5. Write the path where your file is. You can use the one for intranet:
   .../koha/koha-tmpl/intranet-tmpl/prog/en/XSLT/UNIMARCauthResults.xsl
6. Save changes
7. Repeat step 2 and notice the xslt view of results

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>