Bug 18545: Remove use of onclick from OPAC cart

Bug 18545: Remove use of onclick from OPAC cart

To test:
1) Apply patch and add one or more items to your cart
2) Confirm that clicking the following things still works as expected:
 - more details
 - brief display
 - send
 - download
 - print
 - select all
 - clear all
 - selecting by clicking checkbox
 - remove title
 - add title to list
 - place hold
 - add tag
 - empty and close

Sponsored-by: Catalyst IT
Followed test plan, works as expected. Resolves issue with two
print dialogues from Bug 18544.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>