@dzuconni: Going with React. Cleanup +  tests

The cleaned up version of [this PR](https://github.com/artsy/positron/pull/25).

I struggled with tests at first because immediately it was cool and I just used [benv](https://github.com/artsy/benv) and friends like normal. However b/c of the virtual DOM it's not as straightforward when it comes to click/etc. events. I found [this blog post](http://www.asbjornenge.com/wwc/testing_react_components.html) which helped a lot and eventually figured out how to dive inside React components and test them and their virtual DOM.

Started to integrate jade-react. Then realized that's just one too many browserify transforms/levels of abstraction to deal with. Although not ideal for describing markup, coffeescript is terse enough to create something that's IMO more pleasant than JSX/CJSX.

![cap](https://cloud.githubusercontent.com/assets/555859/4648513/d8671ae8-5482-11e4-83ca-09aacfe70aa1.gif)