DB prefill script

Created a script to prefill the database

NOTE: In order to generate users with this script, you should first run
persona-faker (http://github.com/aricha/persona-faker) so that we can
generate fake Persona assertions (instead of flooding the production
Persona server with fake users). You should also update PERSONA_VERIFICATION_URL
in settings_local.js to point to this endpoint (ie. http://localhost:9001/verify)
so that galaxy-api actually touches this server.

Addresses issue #3