Bug 26296: Use new table column selection modal for OPAC suggestion fields

Bug 26296: Use new table column selection modal for OPAC suggestion fields

This patch builds on the change introduced by Bug 22844, changing the
selection mode for the OPACSuggestionMandatoryFields and
OPACSuggestionUnwantedFields preferences to a modal.

This patch includes a database update for converting the format of the
saved values in these preferences. Previously the suggestions table
fields would be separated by a comma. Now they should be separated by a
pipe.

To test, apply the patch run the database update.

 - Go to Administration -> System preferences.
 - Search for 'OPACSuggestion.'
 - The input fields for OPACSuggestionUnwantedFields and
   OPACSuggestionMandatoryFields should appear as "locked" (read-only)
   inputs.
 - Clicking either input field should trigger a modal window with
   checkboxes for each available column in the suggestions table.
 - Test that the "select all" and "clear all" links work correctly.
 - Test that the "cancel" link closes the modal without saving your
   selections.
 - Test that the "Save" button closes the modal, copies your
   selections to the form field, and triggers the preference-saving
   function.
 - Test that changes to both preferences are correctly reflected in the
   OPAC suggestion form.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>