Bug 29369: Use Flatpickr in dateaccessioned cataloging plugin

Bug 29369: Use Flatpickr in dateaccessioned cataloging plugin

This patch udpates the dateaccessioned cataloging plugin to use the
Flatpickr date picker instead of jQueryUI.

To test, apply the patch and open an item for editing in Cataloging.

- The date acquired field (952$d) should have flatpickr styling.
- Clicking in the field should populate the field with today's date and
  trigger the calendar popup.
- Clicking the "..." next to the field should populate the field (when
  empty) with today's date.
- Verify that tabbing from a different field into the date acquired
  field behaves the same as a click.

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>