Return all messages.

Example response

{
  "messages": [
    {
      "appid": 5,
      "date": "2018-02-27T19:36:10.5045044+01:00",
      "extras": {
        "home::appliances::lighting::on": {
          "brightness": 15
        },
        "home::appliances::thermostat::change_temperature": {
          "temperature": 23
        }
      },
      "id": 25,
      "message": "**Backup** was successfully finished.",
      "priority": 2,
      "title": "Backup"
    }
  ],
  "paging": {
    "limit": 123,
    "next": "/message?limit=50&since=123456",
    "since": 5,
    "size": 5
  }
}