Simplification of structural/mvc.py

[Tom Schraitle]

The code from structural/mvc.py can be replaced by a more concise and simpler version:

class Price1(float):
    def __str__(self):
        return "{:.2f}".format(self)

[Sakis Kasampalis]

Hi,

Thanks for the suggestion. Feel free to submit a pull request and I happily approve it.