The Number class and the Calculator app updated

I've updated my Number class, as well as my Calculator for Silverlight that uses it.

I've made the Number class immutable and fixed some other minor issues, and I've fixed a bug in the Calculator that was causing the zeros at the end of a floating-point number to disappear if the Negate button is clicked. The current version of the Number class is 1.5.5, and of the Calculator app - 1.5.

Disclaimer. The Number class is far from finished. I intend to do some work on improving it, but first I might have to brush up on my algorithms. So it's going to be shelved for some time - but it's not going to be forgotten!

Regards,
Boyan