YITH WooCommerce Ajax Product Filter Premium 5.9.0

* New: Support for WooCommerce 4.1
* Update: plugin framework
* Dev: yith_wcan_color_get_objects_in_term to filter the get_product_in_terms function

* New: Support for WordPress 5.4
* New: Support for WooCommerce 4.0
* Update: plugin framework
* Fix: Undefined index prices

* New: Support for WooCommerce 3.9
* Fix: Missing current tag in Stock and On sale filter
* Fix: Not updating filters when the customer apply a filter by price