WIP: filter markers on click category.

#172

Initial state 3 marker, after filter:
![screen shot 2014-12-16 at 5 12 12 pm](https://cloud.githubusercontent.com/assets/2622152/5455731/da047db0-8546-11e4-8226-e79d45076c5b.png)

doc should be under the ``@returns``