Layer switcher

![untitled](https://cloud.githubusercontent.com/assets/6946910/5359993/7017033a-7f8f-11e4-8a35-1af32441f378.png)
![untitled2](https://cloud.githubusercontent.com/assets/6946910/5359997/73ee82bc-7f8f-11e4-9a5c-ba235c39b4ba.png)

* Add toggle button to allow switching of layer views
* Style toggle button
* Add ability to view heatmap in place of markers
* Limit incidents to past month

* Will continue making changes to heatmap(s), etc. in future pull requests
nope, still returns w/o the time piece :/