Bug 27949: Allow multiple article requests print slip

Bug 27949: Allow multiple article requests print slip

This bug allows for batch printing of multiple article requests slips

To test:
1. apply this patch
2. restart_all
3. enable ArticleRequests preference
4. create multiple article requests
5. go to circ/article-requests.pl in staff interface
6. print a single slip from a row
CHECK => it works as expected
7. select all rows and print slip from general actions menu (above the table)
SUCCESS => all article requests slips are printed
8. select multiple rows (not all) and print slip from general actions menu (above the table)
SUCCESS => only selected article requests slips are printed

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
JD amended patch: Perltidy!

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>