Prettier lines

This injects [simplestyle](https://github.com/mapbox/simplestyle-spec/tree/master/1.1.0) properties into the geojson before it's passed to mapbox to add custom style to lines. The style came from [transitmix](https://github.com/codeforamerica/transitmix). This will fix #13.

I also couldn't help myself - I had to do [something about the spacing](https://github.com/ResourceDataInc/last-mile/commit/197aff919c9b13f9fa055f315154abb53d9c7e46) in index.html.

![screen shot 2014-06-21 at 4 34 38 pm](https://cloud.githubusercontent.com/assets/51882/3350179/4c39a5a2-f994-11e3-8f21-323fed564bff.png)