Bug 29229: Use Flatpickr in suggestion search sidebar filter

Bug 29229: Use Flatpickr in suggestion search sidebar filter

This patch corrects the date field configurations for the suggestions
sidebar filter. These fields are now linked Flatpickr widgets instead of
jQueryUI datepickers.

To test, apply the patch and go to Suggestions.

- In the sidebar, click "Suggestion information" to expand the form.
- Test these linked date fields:
  - "Suggested date from" and "to"
  - "Managed date from" and "to"
  - "Accepted by from" and "to"
- Each should trigger Flatpickr calendars which are linked, i.e. you
  can't select a "to" date which is before a "from" date.
- Test that the dates submit correctly to filter as expected.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>