Stop using Garner for caching

It's causing problems on Heroku. Our most time-consuming process was fetching all locations (/api/locations). Instead of fetching the records from the DB, it's now using ElasticSearch to return the data, which never hits MongoDB. Locations are sorted by created_at in descending order (newest first).

I also added localization for the kind and accessibility enumerized fields so that the JSON includes the human-friendly versions.

Nearby radius now defaults to 0.5