JSON output should include GEOID where used

[critzo]

Stats output that includes GEOID fields are intended to support a user re-joining statistics data from the API with geospatial shapes within a GIS application. Though the GEOID is present in the URL, and could be known on an individual basis, in practice mapping applications will have the spatial geographies already, and want to match a field in the JSON output, rather than look up each one based on the URL query.

Adding GEOID to the JSON output will resolve this, and should be fairly easy since it's already in the query output for endpoints like counties and tracts