Add a local/custom db.Table definition for properties

[Aaron Straup Cope]

So that we are only storing/retrieving properties rather than entire features (and their geometries)

• https://github.com/whosonfirst/go-whosonfirst-pip-v2/blob/master/app/indexer.go
• https://github.com/whosonfirst/go-whosonfirst-pip-v2/blob/master/http/intersects.go

The other alternative is to update the geojson table schema in go-whosonfirst-sqlite to store geometries and properties as separate columns/blobs but then it is always left as an exercise to the user to reconstruct the feature...