Polylang for WooCommerce 2.1

Fix variable product removed from the cart when a second browser tab displays the backend
Fix variable product removed from the cart when a REST request occurs on front
Fix shop pages set as child page
Fix PHP warning when the option `woocommerce_bacs_accounts` serialization is corrupted
Fix PHP notice when a user resetting his password has a user locale which doesn’t exist in Polylang

* Fix fatal error on order-received page when no order id is provided.
* Fix the translations status report visible when no languages are defined.
* Fix PHP notice in wizard.
* Subscriptions: fix translated slugs of endpoints not working.
* Subscriptions: fix a conflict with WooCommerce Memberships causing a PHP notice.

* Requires WooCommerce 3.4 or higher, Polylang 2.7 or higher
* Don't allow users without manage_product_terms permissions to create categories using the product importer
* Add a WooCommerce step to the wizard
* Add compatibility with WooCommerce Free Gift Coupons
* Fix new account email sent in wrong language when the language is set from the content
* Fix variation name in "Pay for order" form