private void btnShowVisitorInfo_Click(object sender, EventArgs e)
 {
     if (lbVisitors.SelectedIndex != -1)
     {
         VisitorSearch.ShowVisitorInfo((Visitor)lbVisitors.SelectedItem);
     }
 }
 private void lbVisitors_MouseDoubleClick(object sender, MouseEventArgs e)
 {
     if (lbVisitors.SelectedIndex != -1)
     {
         VisitorSearch.ShowVisitorInfo((Visitor)lbVisitors.SelectedItem);
     }
 }