private async void CoreFlyoutButtonClick(object sender, RoutedEventArgs e)
{
var flyout = new CoreWindowFlyout(new Point(50,50));
flyout.Title = "Sign up";
flyout.Commands.Add(new UICommand("Yes", SaveCommand, 1));
flyout.Commands.Add(new UICommand("No", NoCommand, 2));
IUICommand command = await flyout.ShowAsync();
}