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)

Please use jQuery for its more concise API and cross-browser robustness: `if ($(e.currentTarget).hasClass('yes-btn')`

Note that I'm using `e.currentTarget` instead of `e.target`. The difference is that if there were another element within your button, let's say an icon, and the user clicks that icon, `e.target` would be set to that icon while `e.currentTarget` would be the button, and the latter is usually what you want. This is due to event bubbling — the event takes place on the icon, and bubbles up in the DOM till it reaches a handler (and we placed a handler on the button).