Notification message for `publish` action should contain a `document` attribute with the message

[ballinette]

Since the alignment of notification responses format (#147), notifications for Realtime controller are not well formatted for publish action:
We receive this kind of message:

{
  status: 200,
  roomId: '0e40bdc5ff8fc181aa3342d6011422ed',
  //(...)
   user: { count: undefined }
}

We should receive:

{
  status: 200,
  roomId: '0e40bdc5ff8fc181aa3342d6011422ed',
  //(...)
  document: {
    // a Kuzzle Document with the message content
  }
}