Bug 28373: Add PassItemMarcToXSLT system preference

Bug 28373: Add PassItemMarcToXSLT system preference

Default stylesheets do not reference item fields for XSLT display, however, we
spend time translating the values in the item fields.

This patch adds a system preference, PassItemMarcToXSLT. and unless enabled we remove
item fields before processing

To test:
1 - Perform some search on the staff client and opac
2 - Use the console (F12) to view the time spent on the network tab
3 - Note performance
4 - Apply patch, updatedatabase, restart_all
5 - Repeat searches
6 - Note that display has not changed
7 - Note performance, results should display slightly faster

Signed-off-by: Emmi Takkinen <emmi.takkinen@koha-suomi.fi>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>