Allow voting on reviews

First draft, posting a PR mainly since I have a few questions, and for some early feedback. 
![rate_reviews_1](https://cloud.githubusercontent.com/assets/2644780/3867707/5265ae9c-200b-11e4-83eb-ac71a6d84bc3.png)

These model fields should already have already been ints before being passed via `attrs` in `initialize()`. Thus, it shouldn't be necessary to do `parseInt()`. Even if you needed to parseInt(), you should only do it once in `initalize()` before storing the value on the model.