mvc framework required to implement sponsor_osra_id

part of PT story https://www.pivotaltracker.com/story/show/75999516

- *** This does not create a sponsor_osra_id yet ***
- model with validation that 1 and only one branch or oganisation is selected
- migration to add organization reference to sponsor
- belongs to organization reference in model
- specs to check 1 branch or orgnaization has been selected
- fixed sponsor factory so it is valid against new criteria
- fixed feature files to  reference a branch so they can be valid
- changed active admin form to show the organization and branch drop downs
Its eloquent, I like it.
Whats your opinion on using bitwise operators for logic?
Would we need to make the error message clearer now there is only one?
I'm torn, what do you think?