YITH WooCommerce Brands 2.21.0

* New: support for WordPress 5.4
* New: support for WooCommerce 4.0
* New: added Elementor widgets
* Tweak: code reformat
* Fix: better filter handling for brand names starting with a number or special character

* New: support for WooCommerce 3.9
* Update: plugin framework
* Tweak: added brand rewrite among permalinks optional settings
* Tweak: fix product rewrite, when it only contains %yith_product_brand%
* Dev: added yith_wcbr_change_brand_name_in_filter filter

* New: support for WordPress 5.3
* New: support for WooCommerce 3.8
* Update: Plugin Framework
* Update: Italian language
* Update: Spanish language
* Update: Dutch language
* Fix: prevent error with empty allowed and excluded brands on coupon validation
* Fix: call the correct class for brand_filter static function
* Fix: warning on cart, when brand options for the coupon are empty
* Fix: now filters & pagination behave correctly together on brands_filter shortcode
* Fix: order by name if no filter is selected
* Fix: notice on brand category shortcode