Implements Ogr::Info in other Ogr classes
ProtectedArea importer can now work with stringified keys

This way it is compatible with more database adapters (Sequel produces
symbolized hashes, AR produces stringified)
ProtectedArea importer ignores geometry attributes

Geometries are handled separately by GeometryImporter, as RGeo
performance in the postgis-adapter is too terrible to allow importing
via ActiveRecord here.