Re-import census data, include Pennsylvania

This commit does a lot:

- Turns data/models into a module, so we can add more data types in their own files
- Removes census columns that we aren't going to use in the demo
- Add Pennsylvania to the census imports
- Scripts converting TIGER shapefiles into UTF-8, and combining tracts and block groups from multiple states
- Adds a reset_db.sh, to bring it all together

The import will take a while.  I plan to start it in the morning, so we'll hopefully have data by the meeting.