YITH WooCommerce Waiting List Premium 3.9.0

* New: Support to WooCommerce 3.4.1.
* New: Privacy Policy DPA.

* New: Support to WooCommerce 3.4 RC1.
* New: General Data Protection Regulation (GDPR) compliance.
* New: Option to add a Privacy Policy checkbox to the waiting list form.
* New: Option to enable Double Opt-In subscription method.
* New: Filter by product stock status for Waiting Lists table.
* New: Search by product name for Waiting Lists table.
* New: Search by email address for Waiting List Users table.
* Update: Language files.
* Update: Plugin Core.
* Fix: Bulk action for Waiting Lists table.

New: support to WooCommerce 3.3.4
New: support to WordPress 4.9.4
Fix: add endpoint method
Fix: add product param to email templates filter
Fix: wrong name for custom attributes in waiting list table
Dev: new filter 'yith_wcwtl_recipient_mail_subscribe'
Update: plugin fw