In which we add simple CRUD for linking questions to quests

Yeah, so it's pretty clear that no one ever looks at these, but really the folks working with this API I'm building ought to at least sign off on the API changes even if they can't comment on the code itself.  Look -- I updated the API docs!  Just review that!

Depends on https://github.com/freedomgames/Planet-Lab/pull/16

@maiamcguinness @bunnyblanco