Returning http 401 for requesting too many categories

[TheGreatRefrigerator]

If more than 5 categories are requested, the API returns a http 401 (unauthorized) with response like:

  "message": "Must be one of [100, 120, 130, 150, 160, 190, 200, 220, 260, 330, 360, 390, 420, 560, 580, 620] for dictionary value @ data['filters']['category_group_ids']"
}

This should be an http 500 with internal errorcodes 4001, 4002 etc. similar to directions or isochrones endpoint.

[TimMcCauley]

#15