Bug 22844: Simplify the process of selecting database columns for system preferences

Bug 22844: Simplify the process of selecting database columns for system preferences

This patch introduces a new way for users to select database columns for
system preferences like BorrowerMandatoryField, which currently
require hand-typing of database names.

This new system uses a JSON file containing label:column pairs for
database columns which are relevant to preferences which reference
borrower table columns. My intention was to have user-friendly values as
the labels, but embedding English strings in JSON would make them
untranslatable.

The following preferences are affected:

 - BorrowerMandatoryField
 - BorrowerUnwantedField
 - PatronSelfModificationBorrowerUnwantedField
 - PatronSelfRegistrationBorrowerMandatoryField
 - PatronSelfRegistrationBorrowerUnwantedField

== Test plan ==
 - apply the patches
 - regenerate the staff client CSS (yarn build)
 - updatedatabase
 - dbic
 - flush_memcached
 - restart_all to make sure the updated .pref file is used

 - Go to Administration -> System preferences, and search for
   "PatronSelf"
 - The input fields for PatronSelfModificationBorrowerUnwantedField,
   PatronSelfRegistrationBorrowerMandatoryField, and
   PatronSelfRegistrationBorrowerUnwantedField should appear as "locked"
   (read-only) inputs.
 - Clicking the input field should trigger a modal window with
   checkboxes for each available column from the borrowers 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 (this
   eliminates the need to click a save button again after closing the
   modal).
   - Test this process by making modifications to all three different
     preferences, confirming that the right data is preselected each
     time the modal is shown and the right data is saved to the right
     field each time.

Signed-off-by: Hayley Mapley <hayleymapley@catalyst.net.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>