Clean up code, persist zoom/pan state in URL

Zoom/pan actions will now persist in the URL of this demo app. I also streamlined the code a bit so it's easier to read and modify. Enjoy!

![screen shot 2014-11-05 at 7 55 40 pm](https://cloud.githubusercontent.com/assets/180438/4930699/cbd3d784-6568-11e4-8b65-53a09a804b77.png)