fix(error): Swap out AccessDeniedExceptionHandler for FiatAccessDeniedExceptionHandler

[jonsie]

New message examples:

{
  "timestamp": "2019-09-27T00:05:57.925+0000",
  "status": 403,
  "error": "Forbidden",
  "message": "Access denied to application smalleytest - required authorization: WRITE"
}

{
  "timestamp": "2019-09-26T23:59:59.617+0000",
  "status": 403,
  "error": "Forbidden",
  "message": "Access denied to service account someServiceAccount"
}

Due to these changes:
spinnaker/fiat#474
spinnaker/fiat#475