private void btnPromenaLozinke_Click(object sender, RoutedEventArgs e)
        {
            GlavniPanel.Children.Clear();
            PromenaLozinke pl = new PromenaLozinke(student);

            GlavniPanel.Children.Add(pl);
        }
        private void btnPromenaLozinke_Click(object sender, RoutedEventArgs e)
        {
            GlavniPanel.Children.Clear();
            PromenaLozinke p = new PromenaLozinke(trenutniKorisnik);

            GlavniPanel.Children.Add(p);
        }