Add region-indexing script

[corviday]

Bare-bones functionality: The region-indexing script should accept a shapefile containing one or more polygon or multipolygon features, a database connection string, and a string indicating what kind of region is in the shapefile (basin, watershed, or conservation unit). A region should have a full name and short code, and opionally a point representing the hydrological "outlet" of the watershed.

Desirable bonus features :

• [ ] if a newly indexed region has the same kind and code as an already indexed region, update the existing region instead of creating a duplicate one
• [ ] if the region is a multipolygon, drop all polygons under a certain size - they probably won't have salmon populations and they slow down geometric calculations
• [ ] I have been simplifying regions in QGIS, maybe doing it in the indexing script with shapely for more consistent and trackable results would be smart
• [ ] test indexing

[corviday]

I've been experimenting with the shapely concave_hull command. I think it might be useful to turn islandy shapes with dozens or hundreds of little polygons into polygons more reasonable to do calculations with and display on maps. We don't expect any other watershed to be between islands where it would overlap a concave hull, just empty ocean. Including empty ocean won't impact calculations, since data just isn7t available there..