* Add core breakpoint 480px, remove non-core breakpoints
* Add the optional operator & save callback
* Add the catOperator as a valid attribute
* Enable cat operator for Products by Category
* Add cat_operator support the products API endpoint
* Enable cat_operator in the shortcode and query utils
* Pluralize the “nothing found” string if we have multiple categories
* Fix style in the inspector panel
* Add category operator support to the Best Sellers product block
* Add cat_operator support to On Sale Products block
* Update label & margin