Add MapBox API to Guidr

Install geocoder gem
Create listing.js
Create map params in applicaiton.css
Add latitude and longitude column to listing migration
Add div id map to listing show
Add mapbox and leaflet links to layouts
Update listing model
Add geojson to show method in listing controller
If you don't use e you can leave it out.

```coffeescript
map.on 'layeradd', ->
```