Added support for localization of address fields

Supports different address formats via country code (works similar to imperial units for maxspeed fields)

More countries can be easily added via geojson.io (e.g.: with the poly files found at http://download.geofabrik.de).

An alternative way to get the country code for a location would be a thirdparty service like nominatim or geonames (drawback - server load and latency).
Nice use of rbush for the caching here.

Can you add tests for this module? See the `iD.taginfo` test for an example of mocking server responses.