private void productsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            QuanlyProduct quanlyProduct = new QuanlyProduct();

            addForm(quanlyProduct);
        }
        private void btnQLSP_Click(object sender, EventArgs e)
        {
            QuanlyProduct quanlyProduct = new QuanlyProduct();

            quanlyProduct.Show();
        }