Bug 15485: Use lists-specific XSLT sysprefs

Bug 15485: Use lists-specific XSLT sysprefs

This patch makes the shelves.pl (staff) and opac-shelves.pl scripts
use the new sysprefs for specifying custom XSLTs for lists display.

XSLT.pm is patched so it defaults to the corresponding *Results.xsl
files if none is specified.

To test:
- Create a list
- Open the list in the staff interface
- On a new tab, open the list in the OPAC.
- Apply this patches
=== default behaviour
- Open the list (both opac and staff) on new tabs
=> SUCCESS: They look exactly the same (hint: the syspref is set to ''
   so it should fallback to using the one we were using.
=== using the new functionality
- Create custom XSLTs for lists, for example:
  $ cd /home/vagrant/kohaclone/koha-tmpl/opac-tmpl/bootstrap/en/xslt
  $ cp MARC21slim2OPACResults.xsl MARC21slim2OPACLists.xsl
- Edit your sysprefs, setting OPACXSLTListsDisplay to:
  /home/vagrant/kohaclone/koha-tmpl/opac-tmpl/bootstrap/{langcode}/xslt/MARC21slim2OPACLists.xsl
- Reload the OPAC list view
=> SUCCESS: Looks exactly as before
- Make some minor tweak (for example in line 423 replace
  <xsl:text> </xsl:text>
for
  <xsl:text> BLAH </xsl:text>
- Reload the list
=> SUCCESS: BLAH shows in several places on the title.
- Repeat for the staff interface
- Sign off :-D

So we can now set custom XSLTs for lists.

Sponsored-by: Carnegie Stout Library
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Deb Stephenson <DStephen@dubuque.lib.ia.us>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>