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
nil is falsey. Validates presence of will not work because it uses blank? to test which will turn a falsey value into false. The example I pasted earlier uses validates inclusion in. This uses identity I believe which will prevent nils because.
nil == false -> false
nil == true -> false