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
this makes me uncomfortable. This could be a long discussion.
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- all the major crawlers / search engines respect nofollow
- I still don't like this despite all the above. Were back to the conversation of get requests being idempotent and this is a get request masquerading as a delete request. See safe methods at http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html