Bug 27282: Add window.onafterprint function

Bug 27282: Add window.onafterprint function

TO TEST:
-set up a new list with a few items
-go to /cgi-bin/koha/virtualshelves/shelves.pl and view that list.
-Click 'Print List' in Chrome.
-The tab opens but immediately closes itself.
-Apply patch and clear cache
-Try again, the print dialouge remains open

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>