Make method to get children comments tree

[RTyy]

Method should return json tree that contains all children comments for the specified one.

• Make tests.
• Make simple data validation (required data, incoming data types).

Request:

  "itype_id": instance_type_id,  # id of the instance type (0 or unspecified = comment),
  "i_id": instance_id,  # id of the instance,

curl -i -X GET http://local.server.com/api/comments/tree/{i_id}/{itype_id}/

Responses:

On Success Status Code: 200

[
    {
      "id": comment_id,
      "author_id": author_id,
      "content": comment_content,
      "created": comment_create_date,
      "updated": comment_update_date,
      "parent_id": parent_coment_id or null,
    },
    {
      ...
    }
  ]
}

On Error Status Code: 400, 403, 404

{
  "error": error_title,
  "data_errors": {
     "var_name": error_code,
     ...
  }
}

[RTyy]

Streaming implementation finished. Going to make websocket based one.