Need 404 json for API pages

[abkfenris]

https://sentry.io/alex-kerney/riverflows-docker/issues/286398871/

NotFound: 404: Not Found
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...
  File "flask_debugtoolbar/__init__.py", line 125, in dispatch_request
    return view_func(**req.view_args)
  File "python3.6/cProfile.py", line 109, in runcall
    return func(*args, **kw)
  File "app/api_0_1/samples.py", line 106, in get_sample
    sample = Sample.query.get_or_404(sid)
  File "flask_sqlalchemy/__init__.py", line 422, in get_or_404
    abort(404)
  File "werkzeug/exceptions.py", line 646, in __call__
    raise self.mapping[code](*args, **kwargs)

TypeError: Object of type 'NotFound' is not JSON serializable
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  File "app/api_0_1/errors.py", line 29, in not_found
    response = jsonify({'error': 'not found', 'message': message})

TypeError: Object of type 'NotFound' is not JSON serializable