Add flags for specifying specific geometry sources to index

[thisisaaronland]

For example only "reversegeo" geometries. Uncertain at this time where these hooks should be added or how they filter down to specific implementations (rtree, sqlite, etc.)

Related:

• Indicate which geometry alt should be used for reverse geocoding whosonfirst-data/whosonfirst-data#367
• Add new wof:geom_alt property whosonfirst-data/whosonfirst-data#1793