LearnDash LMS Notifications Addon 1.6.4

* Added - Multi triggers/conditions support
* Added - 'learndash_notifications_subscription_page_slug' filter to modify subscriptions page slug
* Fix - Disable course fields when using quiz trigger
* Fix - Send single email instead of multiple for "User hasn't logged in for X days" trigger when multiple courses are involved
* Fix - Reschedule drip lesson when user enroll date changes
* Fix - "User hasn't logged in for X days" trigger correctly sends to users now
* Fix - Prevent "A scheduled lesson is available to user" notifications sending from wrong course
* Fix - Display specified course lessons in notifications page listing column
* Fix - User receives quiz failed notification when quiz not failed
* Fix - Group leaders not receiving emails for groups they are leaders of
* Fix - Allow group URL in notifications shortcodes

* Added AJAX search support on notifications list posts filter
* Added improve LD posts selector logic especially for site with big number of courses, lessons, etc
* Added change post selectors in notification metabox to use select2 and dynamic AJAX options
* Updated update LearnDash strings using LD custom label
* Updated use learndash_quiz_submitted action hook instead of learndash_quiz_completed
* Fixed make sure retrieved group leaders has group leader role
* Fixed before course expires notification is sent before set value
* Fixed Make sure pre selected value is selected on edit screen
* Fixed group selector returns empty result
* Fixed use learndash_emails_send insteand of wp_mail to sync with LD core
* Fixed before and after expiry notification is not sent when user re-enrolls
* Fixed issue when drip lession triggered for all lessions

* Added a filter to switch the notification content to RTL learndash_notifications_email_rtl
* Updated the trigger "user hasn't logged in for X days" to group the emails into one rather than sending out mass separate emails
* Fixed Notification for drip lesson doesn't update the send time if enrollment date gets changed
* Fixed PHP warnings/notices