RFC Extract Geometries, Widen Geohash coverings, and minor refactoring.

This branch: 
 * widens getUniqueGeohashSubstringsInPolygon to accept Geometries rather than merely Polygons.
 * pulls geometries from actually Filters rather than using FilterToAccumulo.
 * pulls out some of the Filter processing as a trait.
Ah, missed the "RFC" part; sorry 'bout that (SBT).