Rate Calculator

#160 

WIP: This is how it looks right now.

![selection_043](https://cloud.githubusercontent.com/assets/7369740/4268208/8eded28e-3caa-11e4-852b-a366d14bf08b.png)


![selection_044](https://cloud.githubusercontent.com/assets/7369740/4268207/8d4851c0-3caa-11e4-8531-462fc5d1942e.png)