WooCommerce Waitlist 2.4.16

* Fix: Minimum stock amount not working due to typo on option name

* Fix: Users not always removed from waitlists when they make a purchase for the prouct
* Fix: Mailouts are now only sent when the stock level increases
* Added filter for adjustment of time delay between when a user can receive another waitlist notification

* Fix: Error on product page shortcode
* Fix: Duplicate waitlist emails sent out when products set to managing stock