Topic/browse view

This pull request adds support for a browse/search page that updates the results list and map view based on zoom level.

After talking with both Bennet and Kenny, decided to only slightly modify my code to get the functionality right. Kenny noticed a typo in my promises/deferred code that actually fixed what I was trying to do very nicely.

Few things to note:
- moved javascript related to styling to a separate styling.js file
- moved leaflet icons to a separate javascript file
- sets up a more sane location api endpoint -- now takes location_id as an optional parameter. If no location_id is present, returns the list of locations
- adds a management command to export topo/geojson files for neighborhood boundaries