Add date and time a message was created

[JohnMwashuma]

The messaging endpoint (curl -X GET https://api.ona.io/api/v1/messaging?target_type=xform&target_id=[target_id]) is missing two properties, the date the message was created and the time of creation. We also discussed about adding the creators name which is also missing though it is not part of the current deliverables.

Example response from the endpoint :

[
    {
        "id": 1,
        "message": "Extra points to those that finish today!",
        "target_id": 241260,
        "target_type": "xform"
    }
]

Aha! Link: https://ona.aha.io/features/PROD-387