Bug 33568: Move code to a dedicated include file

Bug 33568: Move code to a dedicated include file

Not very nice but at least the code is isolated in a separate file and
reduce the size of detail.tt

We could also move the code related to the item bundle that is included
inside this same table.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Laurence Rault <laurence.rault@biblibre.com>
Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Tomás Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>