WooCommerce Product Search 5.4.0

* Fixed our taxonomy query to exclude products that are out of stock and products excluded from search.

* Fixed warning due to use of deprecated action woocommerce_product_write_panels, now using woocommerce_product_data_panels.
* Fixed warnings where parameter is expected to be a reference but a value is given (related to PHP 7).
* Fixed error "The 'INFORMATION_SCHEMA.GLOBAL_VARIABLES' feature is disabled ..." on MySQL 5.7

* Updated the plugin for WooCommerce 3.0.0 compatibility.