Bug 18540: Handle indexing sort title only when needed

Bug 18540: Handle indexing sort title only when needed

This patch moves the code that generates the xsl for MARC21 biblio sorting
to it's own template that is only called when specified in the xml

To test:
 1 - xsltproc etc/zebradb/xsl/koha-indexdefs-to-zebra.xsl etc/zebradb/marc_defs/marc21/authorities/authority-koha-indexdefs.xml > etc/zebradb/marc_defs/marc21/authorities/authority-zebra-indexdefs.xsl
 2 - git diff
 3 - Note that authority-zebra-indexdefs.xsl now has 245 Title:s info
 4 - Apply patch
 5 - xsltproc etc/zebradb/xsl/koha-indexdefs-to-zebra.xsl etc/zebradb/marc_defs/marc21/authorities/authority-koha-indexdefs.xml > etc/zebradb/marc_defs/marc21/authorities/authority-zebra-indexdefs.xsl
 6 - git diff
 7 - There are lines added about title sort, but no 245 block
 8 - xsltproc etc/zebradb/xsl/koha-indexdefs-to-zebra.xsl etc/zebradb/marc_defs/marc21/biblios/biblio-koha-indexdefs.xml > etc/zebradb/marc_defs/marc21/biblios/biblio-zebra-indexdefs.xsl
 9 - git diff
10 - Note lines changes to ...title_sort
11 - 245 block does not change

Signed-off-by: Hayley Pelham <hayleypelham@catalyst.net.nz>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>