Implement GeoJSON

* Create GeoJSON in Incident model
* Get GeoJSON in homes controller, remove logic from model
* Change JavaScript to accept GeoJSON to create markers
Implement GeojsonBuilder and improve visualization

* Move creation of GeoJSON into separate GeojsonBuilder
* Use different colors for pedestrians/cyclists/both
* Add circle symbol to represent fatalities
Merge pull request #4 from HayleyCAnderson/geojson

Implement GeoJSON

* Add GeoJSON builder and use GeoJSON to show markers
* Use GeoJSON to differentiate between pedestrians and cyclists and show fatalities