WooCommerce Store Credit 4.5.6

* Tweak - Display the tax label when necessary in the order item totals.
* Tweak - Moved the store credit row after the order subtotal in the order details when applying coupons before taxes.
* Tweak - Display the applied coupon code in the cart totals during checkout.
* Fix - Properly display the store credit value with or without taxes in the order item totals.
* Fix - Fixed invalid discount during checkout when applying a coupon before taxes and the items price includes taxes. Only for WC 3.4+.
* Fix - Fixed duplicate entry of the `_store_credit_used` meta when adding a coupon manually in the edit order screen.

* Fix - Fixed invalid discount when applying a coupon before taxes and the items price include taxes.

* Tweak - Include the `store_credit` parameter in the orders data returned by the API requests.
* Tweak - Automatically delete store credit coupons with zero discount after recalculate order totals.
* Tweak - Added compatibility with WC 3.6.
* Fix - Fixed invalid PayPal request when applying an after-tax discount higher than the order subtotal.
* Dev - The method `WC_Abstract_Order->get_total_discount` now includes the store credit discount.