WooCommerce Store Credit 4.5.6

* Tweak - Synchronize the credit used by the orders in batches of 50 orders during the update process.

* Fix - Fixed wrong discount when applying a 'Store Credit' coupon after taxes to a cart which contains subscription products.

* Feature - Apply 'Store Credit' coupons to an order in the admin screens.
* Feature - Apply multiple 'Store Credit' coupons to the same order.
* Feature - Set the payment method to 'Store Credit' in orders paid with a store credit coupon.
* Tweak - Only delete an exhausted coupon when all the orders where it was used are completed.
* Tweak - Restore the credit when the order is cancelled, refunded or fails.
* Tweak - Re-calculate the coupon discounts after updating the order items.
* Tweak - Restore the coupons' credit when necessary on updating an order.
* Fix - Fixed 'invalid coupon' error when cancelling the payment with PayPal.
* Fix - Fixed wrong discounts for coupons applied before taxes in WC versions between 3.2.2 and 3.3.5.