Bug 25238: Fix semantic heading for opac-details

Bug 25238: Fix semantic heading for opac-details

Prior to this patch the opac-details view contained multiple h1 level
headings.

Test plan
1/ Perform a search in the OPAC that will yield results
2/ Navigate to any results detailed view
3/ Inspect the page and note that two H1 level headings are present
(Page title + Item title)
4/ Apply the patch
5/ Reload the page
6/ Inspect the page and ntoe that the 'Item title' is now a level 2
heading
7/ Note the page still appears nicely
8/ Signoff

Bonus points: Check with XSLT views enabled and disabled, MARC21,
UNIMARC and NORMARC variations.

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>