All Products for WooCommerce Subscriptions 6.0.4

* Tweak - Match plan and apply discounts when manually adding products to active Subscriptions.

* Fix - Fixed switch subscription link for variable products that belong to a grouped product.
* Fix - Renamed the add to cart button, from 'Sign up now' to 'Switch subscription', when in switching context.
* Fix - Improved handling of express checkout buttons for PayPal, Stripe and WC Payments.
* Fix - Use the correct number of arguments for 'raw_woocommerce_price' and 'formatted_woocommerce_price' filters.
* Fix - Improved validation of values when getting maintenance and dismissed notices from the DB.

* Fix - Important: Security improvements.
* Fix - Resolved a compatibility issue with Gravity Forms.