private void LoginLogoutMenuFlyoutItem_Tapped(object sender, TappedRoutedEventArgs e)
        {
            if (IsLoggedIn)
            {
                if (LogoutTapped != null)
                {
                    LogoutTapped(this, e);
                }

                if (LogoutCommand.CanExecute(Header))
                {
                    LogoutCommand.Execute(Header);
                }
            }
            else
            {
                if (LoginTapped != null)
                {
                    LoginTapped(this, e);
                }

                if (LoginCommand.CanExecute(Header))
                {
                    LoginCommand.Execute(Header);
                }
            }
        }