Allow to set the created_at time when creating private comments on an idea via API

While setting the "created_at" attribute when creating public comments for ideas via the API works smoothly, the same doesn't work for private comments. The endpoint used is https://quintly.aha.io/api/v1/ideas/<IDEA_ID>/comments as a POST request with the following JSON as an object (I used sample data here as an example). You can quickly validate that instead of using the date provided with "created_at" it does always use the current date/time instead. Expected is it does use the provided "created_at" attribute as the creation time for this private comment.

{"comment":{"body":"<p>test!<\/p>","created_at":"2016-12-03T17:17:09.296Z","user":{"email":"test@test.com"}}}