Update import scripts to new model

This builds on top of #112 by updating the import scripts to use the new models.

There are several hacks here as the data schema in the files doesn't quite match what is stored in the database. This is a temporary solution until we rewrite based on the hierarchies in usa.gov

Some notes:
* if an agency has only one "office", that office's contact information is set on the agency and no "office" is created
* strings which were combined when creating the data files are separated (e.g. phone number + name)
* probably best to wipe your current db to remove offices which no longer exist