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 did a quick test. Without `numericality: { only_integer: true}` you can assign a character string for instance to the code and it will saved in the db as 0.