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
From a rails helicopter perspective we have 3 main ways to change the database.
1. Standard model interactions
2. Interactions that skip validations either through or external to the model
3. By something external to ruby / rails

Validations are only going to cover point 1. Enforcing at the database level covers points 2 and 3. Agile suggests don't over engineer. However, I have been burned by this before. I think we have to question why we are using a relational database if this is not important.