private void OpenNewCustomerForm()
        {
            var form = new NewCustomerForm {
                MdiParent = this
            };

            form.Show();
        }
        private void NewAndSaveButton_Click(object sender, EventArgs e)
        {
            var form = new NewCustomerForm()
            {
                TopMost = true
            };

            form.Save += SaveInvoice;
            form.ShowDialog();
        }