Bug 27256: Update click handler for point of sale

Bug 27256: Update click handler for point of sale

This patch updates the click handler to bind to the table element in the
DOM as aposed to the individual buttons by their classes. We then use
the event propogation and filter on the button class to catch the clicks
we want.

Test plan
1/ Add 22 debit_types that can be sold to the system (or reduce the
datatable paging size)
2/ Confirm that items on the second page of results cannot be added for
sale on the point of sale page.
3/ Apply the patch
4/ Confirm items from the second table page can now be added correctly
5/ Clicking add when navigating to such an item should leave the items
table unmodified.
6/ Clicking aa when the table was filtered should reset the filters
bringing the table back to the first page
7/ Signoff

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>