void OnTemperatureOptionPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            OptionViewModel <Temperature> option = sender as OptionViewModel <Temperature>;

            if (option.IsSelected)
            {
                this.CupOfCoffee.Temperature = option.GetValue();
            }
        }
        void OnDrinkSizeOptionPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            OptionViewModel <DrinkSize> option = sender as OptionViewModel <DrinkSize>;

            if (option.IsSelected)
            {
                this.CupOfCoffee.DrinkSize = option.GetValue();
            }
        }