Feature/remove userid from uri

Yeah, I don't think we really need /users/<id>/ in front of all our URI's, and they also start to make less sense on many-to-many relationships -- in /users/<id>/missions/<id>/quests/<id> is that user supposed to be the owner of the mission, the quest, or both?

Depends on https://github.com/freedomgames/parklab/pull/10

@maiamcguinness @wilhow