YITH WooCommerce Added to Cart Popup Premium 2.27.0

* New: Support for WooCommerce 4.0
* New: Support for WordPress 5.4
* New: Greek translation
* Update: Plugin framework
* Update: Language files
* Fix: Prevent fatal error "Call to a member function get_formatted_name() on boolean"
* Fix: Discount row visible also if discount amount is zero
* Fix: Empty popup after removing last product
* Tweak: Close popup with "ESC" key

* New: support to WooCommerce 3.9
* New: support to WordPress 5.3.2
* Update: plugin framework
* Dev: new JS trigger 'yith_wacp_cart_counter_updated'

* Update: Notice handler
* Update: Plugin framework