Phase 1 of implementing prizes

Scaffolding for prize_providers, prizes, teacher_prizes, and teacher_bonus_prizes
DB migrations for all of the above
DB migration to add the following to users: prize_earned, prize, teacher_prize_earned, teacher_prize, teacher_bonus_prize_earned, and teacher_bonus_prize
Logic added to properly flip the booleans for prize_earned, teacher_prize_earned, and teacher_bonus_prize_earned

Not yet implemented:
Loading prizes and prize_providers into the tables
Sending e-mail when a prize has been earned
User experience to claim prizes
Enforcement that prizes should be US only
etc.