Polylang for WooCommerce 2.1

* Fix wrong subject & heading language for emails sent in bulk
* Fix wrong translation url when the shop is not translated
* WC Subscriptions: Fix translated variations not deleted when deleting a subscription variation.
* WC Composite Products: Fix fatal error when creating a new translation when the plugin WC Product Search is activated
* WC Composite Products: Fix PHP warnings

* Fix paged shop pages redirected to main shop page (introduced in 1.3.1)

* Requires PHP 5.6 or higher, WordPress 4.9 or higher, WooCommerce 3.2 or higher, Polylang 2.6 or higher
* Change text domain from 'pllwc' to 'polylang-wc'
* Add compatibility with WooCommerce 3.9
* Add compatibility with WooCommerce Composite Products
* Add compatibility with Checkout Field Editor for WooCommerce
* Add compatibility with "All Reviews" block introduced in WC 3.8. Requires Polylang Pro 2.6.9+
* Add compatibility with "All Products" block introduced in WC 3.9
* Duplicate media if they don't exist when translating a product gallery
* Fix jQuery undefined if a user decides to load jQuery in the footer
* Fix duplicated sku error when creating a product translation with the REST API
* Fix "On sale products" block. Requires Polylang Pro 2.6.9+