private void Button_change_Click(object sender, EventArgs e)
        {
            Payment newPayment = new Payment(Int32.Parse(textBox_amount.Text), DateTime.Parse(datetime_due_date.Text), textBox_description.Text, Boolean.Parse(comboBox_paid.Text.Equals("Yes") ? "true" : "false"));

            if (payment.Equals(newPayment))
            {
                MessageBox.Show("Nothing has changed.");
                return;
            }

            controller.Change(payment, newPayment);
            payment = newPayment;

            MessageBox.Show("Payment has changed");
        }