Add methods to photo obj. and improve response

Add the following methods:
* size: get different photo sizes available.
* originalSize: get the original photo size.
* geoData: get the location info available. If there’s no such info,
return a location object with None values in his attributes.

Also, the modification in parse_response allows to return an empty
location.
Merge pull request #1 from estebanz01/master

Add methods to photo obj. and improve parse_response