public void TaBortAlumnKonto(object commandParameter) //Klar
        {
            Alumn.TaBort();
            GLOBALSWPF.AktuellAlumn = null;
            MainWindow loginWindow = new MainWindow();

            foreach (var window in Application.Current.Windows)
            {
                if (window is MainAlumnWindow x)
                {
                    x.Close();
                }
            }
            loginWindow.Show();
        }