Sponsorship functionality & UI

PT story https://www.pivotaltracker.com/story/show/78039462

- Add functionality to link sponsor & orphan (i.e. create sponsorship)
- Sponsored orphans shown on sponsor's page
- Sponsorships can be ended by clicking link next to orphan's name on sponsor page
- Establishing a sponsorship marks orphan as 'Sponsored'
- Only Active Unsponsored orphans displayed when creating new sponsorship link
- Only one sponsorship relationship can be established between a sponsor and orphan (enforced in db)

UI is not final as client has sent new specifications
I did think about how you built up sponsor and was going to comment on it, but left it in the end. I felt it was being picky and we didn't really make much difference in the end which way we did it. 
Really my issue is that rest is meant to be clear and it looks like the last param is a param for sponsorships not for orphans (see my comment below when I got to your routes file)