private void Button_Click(object sender, RoutedEventArgs e)
{
user.Login = registerpage.login.Text;
user.Password = registerpage.password.Text;
user.Firstname = registerpage.firstname.Text;
user.Lastname = registerpage.lastname.Text;
Mysql bdd = new Mysql();
bdd.AddUser(user);
registerpage.NavigationService.Navigate(new RegisterPage());
throw new NotImplementedException();
}