public ActionResult RemoveFromCart(int?id, int?quantity)
        {
            if (User.Identity.IsAuthenticated)
            {
                int customerID = db.Customers.Where(x => x.Username == User.Identity.Name).First().CustomerID;
                db.usp_RemoveFromCart(id, customerID, quantity);
            }

            return(RedirectToAction("Index", "Shopping", null));
        }