WooCommerce Checkout Add-Ons 2.7.4

* Fix - When moving add ons to another position at checkout, ensure that enhanced select and file add ons are re-initialized upon checkout update

* Fix - Ensure that XML exports with checkout add ons data do not contain extra empty tags

* Fix - Address a rare issue where add-ons were sorted in an unexpected order
* Misc - Add support for WooCommerce 3.6
* Localization - Add Italian translation