LearnDash LMS WooCommerce Integration Addon 1.9.8.1

* Added dependencies check
* Added WPML multi language course selector support
* Added background course enrollment warning above course selector field
* Added WC subscription switching feature support
* Updated allow retroactive tool to process course enrollment directly instead of storing the queue in DB
* Updated remove old code that process retroactive tool using cron
* Updated change learndash_woocommerce_silent_course_enrollment_queue option to be non autoload to improve performance
* Updated Use custom label if set
* Fixed renewal process unenroll and reenroll users to courses
* Fixed PHP notice error because of deprecated class property
* Fixed retroactive tool reset enrollment date to the tool run date

* Added group access update functions
* Added group selector field in WooCommerce edit product page
* Added filter hook to reset subscription course access from
* Added filter hook to configure silent course enrollment queue processing count
* Fixed add array typed variable to prevent PHP warning error
* Fixed param check logic to prevent fatal error

* Added subscription parameter to remove course on billing cycle completion filter hook
* Added filter hook to customize retroactive tool per batch value so users can change it depending on their server specifications
* Added process enrollment queue 1 at a time to prevent timemout error
* Added WC requires and tested headers
* Added silent course enrollment feature to prevent long loading time in products with many associated courses
* Added reduce minimum products count for background course enrollment because it caused timeout error
* Updated plugin name and description to match with other addons
* Updated change assoicated course field label
* Fixed fatal error `WC_Order_Refund` object not having `get_customer_id()` method `use get_user_id()` instead
* Fixed CSS issue where `select2` dropdown is missing
* Fixed learndash WooCommerce cron hook not registered