private void addCategoryItemButton_Click(object sender, EventArgs e)
        {
            this.Hide();
            CategoryForm aCategoryForm = new CategoryForm();

            aCategoryForm.Show();
        }
        private void categoryStockOutButton_Click(object sender, EventArgs e)
        {
            CategoryForm categoryForm = new CategoryForm();

            this.Close();
            thread = new Thread(OpenCategoryForm);
            thread.SetApartmentState(ApartmentState.STA);
            thread.Start();
        }