This is a sub-issue of the longstanding #113 Geo* cleanup. WGS84 is implied (and used in the specs ours was based on) but wasn't mentioned. Also GeoCoordinates is hard to re-use / extend in extensions since address was a property of a Place that had the GeoCoordinates as value of a 'geo' property. We should allow the simple option of a GeoCoordinates directly carrying 'address' property.