@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)
Working with the vanilla sections data here. The reason initially is 1. it was more straightforward with what React's docs showed and 2. when the article was syncing with the server in other parts of the apps the `sections` that the React app was using were no longer the same as the one on the Backbone model.

I might decide to use an actual Backbone collection in the React app later, but right now it basically re-injects the vanilla sections data on save as you can see in line 34 above.