[mod] add general purpose JSON api

Extends the JSON API used by fullcalendar with additional fields (location, separated title and source) for general purpose use of the API.

```json
{
    "allDay": false,
    "end": "2013-09-21 14:00:00",
    "start": "2013-09-21 11:00:00",
    "color": "#3A87AD",
    "title": "Journée du Logiciel Libre",
    "url": "http://www.agendadulibre.be/events/196",
    "source": "agenda_du_libre_be",
    "agenda": "be",
    "textColor": "white",
    "location": "Saint-Josse, Bruxelles-Capitale"
}
```