WooCommerce Order Status Manager 1.15.4

* Fix - Ensure Font Awesome icons are loaded on orders list page when HPOS is enabled
* Fix - Ensure order line items appear in custom emails that are dispatched when a new order is created
* Fix - Address PHP warnings when emails are sent
* Fix - Ensures custom image icons are kept in place when status changes are made

* Fix - Do not query order refunds when generating download permissions in upgrade routine

* Misc - Require PHP 7.4 and WordPress 5.6