protected void btn_create_game_Click(object sender, EventArgs e)
    {
        Spieler sp = new Spieler();
        string Gamename = txtGameName.Text;
        string Creator = User.Identity.Name;
        int Gameid =    sp.opengame(Gamename, Creator);
        Session["GameId"] = Gameid;
        Response.Redirect("Spielfeld.aspx");
    }