Bug 7076: Lists render OPAC XSLT on staff side

Bug 7076: Lists render OPAC XSLT on staff side

Adds a small check in C4::VirtualShelves::Page::shelfpage to only render
OPACResultsXSLT if the $type is 'opac'.  Since parsing the XML is such an expensive
thing, and the resulting XSLTBloc is not used on the staff side, this will increase
performance for Lists in the intranet

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
(cherry picked from commit a0a9368beccd1748e720966f25869259a30e68f2)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>