Product Filters for WooCommerce 1.4.35

* Tweak - Change columns implementation to use CSS Flexbox Layout.
* Tweak - WooCommerce 6.5 and WordPress 6.0 compatibility.

* Fix - Prevent error on PHP 8+ from improper return value to `uasort()`.
* Tweak - Bump minimum PHP version to 7+.
* Tweak - Bump minimum WooCommerce version to 3.9+

* Dev - Add .nvmrc file.
* Dev - Update JS minification process for better compatibility with various versions of Node/NPM.
* Fix - use more specific CSS classes to prevent conflicts with other plugins and themes.