private void butContinue_Click(object sender, RoutedEventArgs e)
        {
            LogInWindow loginWin = new LogInWindow();

            loginWin.Show();
            this.Close();
        }
        private void butSignup_Click(object sender, RoutedEventArgs e)
        {
            var user = new UserClient();

            using (var db = new DB())
            {
                try
                {
                    user = new UserClient()
                    {
                        Name             = fldName.Text,
                        Surname          = fldSurname.Text,
                        PassportNumber   = fldPassportNo.Text,
                        UserLogin        = fldLoginUp.Text,
                        Password         = fldPasswordUp.Text,
                        Email            = fldEmail.Text,
                        RegistrationDate = DateTime.Now.ToString()
                    };
                }
                catch (ArgumentNullException ex)
                {
                    MessageBox.Show(ex.Message);
                }
                db.UserClients.Add(user);
                db.SaveChanges();

                LogInWindow loginWin = new LogInWindow();
                loginWin.Show();
                this.Close();
            }
        }