Bug 25801: Add itemnumber parameter to opac-detail

Bug 25801: Add itemnumber parameter to opac-detail

Note: The GetItemsInfo call is now suboptimal. Leaving it as-is
for now in the hope that item refactoring picks it up ;)

Test plan:
Test opac-detail via biblionumber (regular use).
Test opac-detail by passing an itemnumber in the URL:
    /cgi-bin/koha/opac-detail?itemnumber=999

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>