No longer check class_exists(), we shouldn't load this file twice and also other plugins or so shouldn't define this class.
Removed the $db var, we can use the global $wpdb var directly, i think this is a more common way to use the WP database object.
No longer add comment in the extend function, wasn't handy.
Removed midline tab use.
Removed the extend function from this page, will now be part of the WordPress comment system.
Removed the extend function from the admin, will now be part of the WordPress comment system.
Use the DateTime modify function, much easier, cleaner and more readable.
No need to use DateTime class/object for simple NOW() date.
Adjusted comment.
Moved the extend subscription function to the WordPress comment system.