Re-worked user API to show a merge of user and user_detail records.

- From outside the API, it now appears that there's simply one large
  record that is a "user", even though behind the scenes that data is
  split between two tables. Not all models will be grouped like this,
  but it makes sense in this case. The only reason for splitting the
  data is because of backend database concerns. Joining it shortly after
  that makes the rest of the pipeline, both client and server side,
  simpler.