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
@motasem-salem   for model validation I vote for db validation. if there is resistance to it I don't mind only model validation. However having some things we validate at the db level and not others is something I am quite strongly against.