static void Main(string[] args)
        {
            var customerManager = new CustomerManager();

            customerManager.Add(new Customer()
            {
                Id = 4, FirstName = "Afet", LastName = "Agayeva"
            });
            customerManager.Update(new Customer()
            {
                Id = 4, FirstName = "Afet", LastName = "Valiyeva"
            });
            customerManager.Delete(new Customer()
            {
                Id = 4
            });
            //customerManager.Clear();
            foreach (var customer in customerManager.GetAll())
            {
                Console.WriteLine("{0} {1} {2}", customer.Id, customer.FirstName, customer.LastName);
            }

            var customers = customerManager.GetByName("VUQar");

            Console.WriteLine("{0} {1} {2}", customers[0].Id, customers[0].FirstName, customers[0].LastName);
        }