private void BtnTraceSr_Click(object sender, RoutedEventArgs e)
{
lblTraceinfo.Content = btnTraceSr.Content;
listTraceSr = PanelTrace_db.PobierzTraceSr();
grdTraceDane.Children.Clear();
panelTraceSrednice = null;
panelTraceSrednice = new PanelTraceSrednice(listTraceSr);
grdTraceDane.Children.Add(panelTraceSrednice);
}