retrieve:
Return the details about the given Theme id.

list:
List all Theme objects.

GET /api/v1/themes/?offset=10
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "count": 11,
    "next": null,
    "previous": "http://actu.epfl.ch/api/v1/themes/?limit=10",
    "results": [
        {
            "id": 7,
            "fr_label": "Société/Culture",
            "en_label": "Culture",
            "de_label": "Gesellschaft/Kultur"
        }
    ]
}