Bug 11826: Use the XSLT handler in C4/XSLT module

Bug 11826: Use the XSLT handler in C4/XSLT module

Incorporate the new object into C4/XSLT module.
The handler object needed one adjustment to allow for passing URLs.
Removed the GetURI function; it is no longer needed.
Added some documentation lines.
Moved a file-level lexical upwards in the code for visibility.
Removed some tabs (on two lines).

Note: The handler could perhaps be moved up to the Context module, or
be saved in a global ('our') variable.  But I would rather not do that
now, making testing not too complex at this moment.

Test plan:
Enable XSLT preferences for opac and intranet.
Check result and detail pages.
Check individual list display (virtual shelves).
Force an XSLT error by editing one of your xsl files. Check the
corresponding display.
Put an URL in one the XSLT prefs (could just be to your own server).
Check the display.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Running XSLTParse4Display in a loop showed no significant performance
change.
One pass cost me around 0.012 sec (except for the first pass).

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Results, detail, url and list view Ok
No koha-qa errors

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>