Bug 27883: (follow-up) Make label match input id

Bug 27883: (follow-up) Make label match input id

This change alters the list of columns under "Preserve existing values,"
changing the label for each checkbox can be clicked to trigger the
checkbox change.

To test, apply the patch and refresh the patron import page. Expand the
"Preserve existing values" section and click any label in the list. The
corresponding checkbox should be checked.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>