private void AddMenuItem_Click(object sender, RoutedEventArgs e)
        {
            var  ted = new TransponderEntryDialog();
            bool?res = ted.ShowDialog();

            if (res.HasValue && res.Value)
            {
                TLookup.Add(ted.Code, ted.Startnummer);
            }
            MenuItem_Click(sender, e);
        }
        private void RemoveMeuItem_Click(object sender, RoutedEventArgs e)
        {
            var  ted = new TransponderEntryDialog();
            bool?res = ted.ShowDialog();

            if (res.HasValue && res.Value)
            {
                if (!string.IsNullOrWhiteSpace(ted.Code))
                {
                    TLookup.Remove(ted.Code);
                }
                else if (ted.Startnummer != 0)
                {
                    TLookup.Remove(ted.Startnummer);
                }
            }
            MenuItem_Click(sender, e);
        }