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
As above, I find this overly long. Recommend breaking up into
```ruby
it { is_expected.to validate_numericality_of(:code).only_integer }
it { is_expected.to ensure_inclusion_of(:code).in_range 0..99 }
```