~bundle: Replacing mongoid_geospatial with geocoder as the latter has
 nice support for geocoding, seems to be more actively maintainted and
 more compatible with the surrounding frameworks.
Merge branch 'master' into topic/geocoder

Conflicts:
	Gemfile.lock
	app/models/spot.rb
There's a new BaseSerializer which handles MongoDB ID serialization
without $oid. The other serializers inherit from it.
~bundle: Added dotenv-rails for reading environment variables (such
as our geocoder API keys) from an .env file. This file is added to
.gitignore as long as we haven't decided to have public API keys for
development.
The new route /search will save the query, run Geocoder.search,
save the results and return them as JSON.