Multiple claimants:
  - Only recognise routes explicitly managed by ClaimTransitionManager.
    Before unrecognised routes would 500 because the corresponding
    form class didn't exist. Now 404.
  - Fix routes so that they're hyphenated, e.g. /apply/additional-information
    fixes #296
  - Forms always PUT to the same URL as for GET, e.g /apply/claimant
  - MultiplesController, a subclass of ClaimsController is used to
    support non-destructive addition of claimants
  - Allow a la carte destruction of addtional claimants
  - Destroy all additional claimants if the user chooses "No"