[WIP] Use source geometry

 * [x] Make it possible to add a GeoJSON geometry to any source and have it rendered.
 * [x] Switch to a whole-world render up top instead of just US:
    
    ![world](https://cloud.githubusercontent.com/assets/58730/5426302/f1cae880-82fd-11e4-93b4-fa032e32e664.png)