Pretty print API responses

[yazinsai]

Instead of returning this:

{"error":{"type":"processing","code":"bad_request","message":"Bad Request","extras":{"time":"2018-03-14T08:18:23Z","request_id":"d60a4858-1757-4a78-ab18-5d81be7d39b5"}}}

It should return a more readable output like the below:

{
  "error": {
    "type": "processing",
    "code": "bad_request",
    "message": "Bad Request",
    "extras": {
      "time": "2018-03-14T08:18:23Z",
      "request_id": "d60a4858-1757-4a78-ab18-5d81be7d39b5"
    }
  }
}