private void addNannyButton_Click(object sender, RoutedEventArgs e)
{
string id = bl.getLastNannyID();
int newID;
int.TryParse(id, out newID);
newID++;
bl.addNanny(new Nanny((newID).ToString(), 21));
//option 0, the PL has another BindingList
//Problem : PL responsibility
// NannysList.Add(new Nanny((newID).ToString(), 21));
//option 0, ver 2
RefreshWindow();
}