private void BtnNodeGroupLink_Click(object sender, RoutedEventArgs e)
        {
            var frm = new NodeGroupLink();

            frm.ShowDialog();
            DisplayNodeGroupLinks();
        }
        private void MnuEditNodeGroupLink_Click(object sender, RoutedEventArgs e)
        {
            NodeGroupLink frm;

            if (lstNodeGroupLinks.SelectedIndex >= 0)
            {
                frm = new NodeGroupLink(models.AppState.State.GroupLinks[lstNodeGroupLinks.SelectedIndex]);
            }
            else
            {
                return;
            }

            frm.ShowDialog();
            DisplayNodeGroupLinks();
        }