Bug 7626: Delete multiple tags in OPAC at once

Bug 7626: Delete multiple tags in OPAC at once

This patch removes the individual 'Delete' buttons for every tag as
suggested in Comment 0. It adds a checkbox to every tag, with a 'Delete
selected tags' button at the bottom of the table. This patch also adds a
function to check if any checkboxes have been checked before submitting
the form (only works with JS enabled).

To test:
1) Find a record in the OPAC and add some tags to it
2) Go to your tags and notice the checkboxes, no more delete buttons for
each tag
3) Click 'Delete selected tags' button without selecting any tags
4) Confirm alert shows up. Click OK
5) Select one or more tags and click 'Delete selected tags' button
6) Confirm delete is successful and correct number of deleted tags shows
up

Sponsored-by: Catalyst IT
Followed test plan, works as expected
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>