Quick fixes to get UrbanSim running on block group-based skims

moved juan's new functions read_datastore() and geoid_to_zone_map() to utils/io.py and utils/geog.py, respectively.
replace zone mapping func in usim.preprocessor with geoid_to_zone_map()
remove region_zone_skims setting from settings.yaml
augment urbansim skim processing to replace zone IDs if skims are block or block group-based
enable new usim command-line arg skim_source
add method args to enable block model HLCM estimation outside of PILATES

ual / PILATES