LearnDash LMS Notifications Addon 1.6.4

* Updated delay field unchangeable for edit to prevent issue with delayed emails
* Updated use of global delete function instead of create new queries in delete functions
* Updated remove `learndash_notifications_delete_delayed_emails_when_unenrolled` hooked function because it already exists in `includes/database.php`
* Updated use of `learndash_get_users_for_course()` to pull course users instead of access list meta only
* Fixed lesson available notification not queueing multiple notifications in DB if there are more than 1 notifications posts
* Fixed regex pattern for searching notifications by shortcode data key value pair

* Added trigger for after the course expires
* Added filter hooks for custom trigger and functions
* Added course ID and lesson ID to the notification setting fields for upload and approved assignment trigger
* Added status tab to the notifications menu
* Added translation class
* Added cron function to update lesson available notification in the database
* Added default blank value to the AJAX empty select option

* Fixed SQL syntax error
* Fixed assignment essay comment left trigger
* Fixed scheduled notifications to be sent only after the notification timestamp passes the current timestamp
* Fixed lesson and topic URL shortcode returned values
* Fixed logic to exclude unenrolled users
* Fixed logic to prevent sending notification is ID is not numeric

* Updated default comment notification to be disabled for assignment and essay
* Updated SQL in CRUD functions
* Updated delete delayed emails to hourly cron
* Updated send scheduled emails function
* Updated group leader recipient logic
* Updated course completed check to enroll course notification trigger
* Updated lesson available notifications to prevent sending multiple times
* Updated and removed course completed check on essay graded notification
* Updated lesson available scheduled emails function
* Updated dequeue autosave for notification post type
* Updated to hide minor and miscellaneous publishing action widget for notifications
* Updated user deletion LeanrDash data cleanup to hourly cron

• Added submit disabled fields function
• Updated course expiration notification to hourly cron
• Updated legacy notification blank fields hidden
• Fixed error notice