private void Click_Valider(object sender, RoutedEventArgs e)
{
newContact.Nom = TextBoxNom.Text;
newContact.Prenom = TextBoxPrenom.Text;
newContact.Telephone = TextBoxTel.Text;
contacts.Add(newContact);
List <Contact> tmpList = new List <Contact>();
tmpList.AddRange(contacts);
ListContacts.ItemsSource = tmpList;
newContact.SaveContact();
ClearForm();
}