* Fix - Fatal Error when checking out with Checkout Field Editor extension active.
* Fix - Pre-Order fee not applying to variable products.
* Fix - Fatal error when trashing some products.
* Fix - Prevent fatal errors when switching an order to "Pre ordered" without a pre-order product.
* Tweak - Fix wording of release date within confirmation emails when no release date is set.
* Tweak - Add Additional Content text to applicable Pre-Order emails.
* Tweak - Add "Pre-ordered" status to WC reports statuses for revenue reporting.
* Tweak - Use native wp_timezone_string() to retrieve WP timezone setting.
* Tweak - Check that order exists when updating payment complete status to avoid fatal errors.
