Rename `lat` and `lon` fields to `latitude` and `longitude`
For easier compatibility with Geocoder gem
Geocode addresses automatically using Google geocoding API
* it geocodes location only when latitude and longitude coordinates aren't provided
* add a FakeGeocoder object for clear tests. We could use Geocoder built-in solution
but it makes the tests obscures and harder to understand as the expected coordinates
of an address, are set somewhere else, far from the test itself.

https://github.com/alexreisner/geocoder#testing-apps-that-use-geocoder
https://trello.com/c/wbTFtHx9