Doc viewer app

This allows users to open and share a link to exactly one document. Closes #717 

![screen shot 2014-12-04 at 4 26 24 pm](https://cloud.githubusercontent.com/assets/1250387/5308264/601368f4-7bd2-11e4-8cd5-d7f533b0e9d3.png)

This isn't actually being compiled. Also, there doesn't appear to be any rules in `plugins/doc/styles/main.less`.