Added a simple 404 page.

# Changes
- Added a simple 404 page using the styles added in #71.

# Screenshot
![screen shot 2014-11-13 at 12 50 55 pm](https://cloud.githubusercontent.com/assets/583202/5033431/b5ce8cf6-6b33-11e4-9c84-e3a2e33ccc96.png)