Bug 36326: Fix batch item mod/del access from biblio detail page

Bug 36326: Fix batch item mod/del access from biblio detail page

Allow both $op eq "show" and "cud-show".
We need to keep the POST when we upload a file, but we can simply allow
GET with "show".

Test plan:
Go to the biblio detail page, select an item and test both tools via the links
"Delete selected items" and "Modify selected items"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>