private async void Form1_Shown(object sender, EventArgs e)
        {
            ChinookEntities context = new ChinookEntities();
            List<Customer> seznamZakazniku = new List<Customer>();

            await Task.Run(() =>
            {
                seznamZakazniku = context.Customers.ToList();
            }
            );

            dataGridView1.DataSource = seznamZakazniku;
        }