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'm not sure @sampritipanda does not like db:setup because it calls db:seed but we call it in the code anyway.
db:schema:load is meant to be much more efficient than db:migrate especially as the schema grows.
I guess if we don't have a consensus we leave it as is.