Bug 24052: Rename XSLT_Handler

Bug 24052: Rename XSLT_Handler

Should be XSLT::Base now.
Removes old XSLT_Handler stub too (from bug 23290).
Result of a git grep | sed statement.

Test plan:
Run qa tools (so modules compile).
Run t/db_dependent/Breeding.t
Run t/db_dependent/Koha/XSLT/Base.t (This test fails when only this patch
has been applied; see subsequent patch.)
Enable XSLT use on results and details display. Check search results and
detail view on OPAC and staff.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>