Add OSRA Branches

PT Story: https://www.pivotaltracker.com/story/show/77972984

- [x] Added Branch model and seed data
- [x] Added Branch specs and factory
- [x] Added relationship between Sponsor and Branch
I think you need it anyway. The discussion were having about whether we do additional db validations creates at least one common theme amongst everyone.
The models should be the one source of truth. Leaving the integer declaration out seems to me to contravene that.