Return an array where each entry is an object with this form:

{ source: "fitbit", name: "Fitbit", usernames: ["beau", "madprime"] }

GET /api/public-data/members-by-source/?source=direct-sharing-161
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Content-Type: application/json
Expires: Fri, 22 Feb 2019 05:52:01 GMT
Vary: Accept

{
    "count": 34,
    "next": null,
    "previous": null,
    "results": [
        {
            "source": "direct-sharing-161",
            "name": "lineage",
            "usernames": [
                "gedankenstuecke",
                "apriha",
                "madprime",
                "beau",
                "blackbearnh",
                "arvkevi",
                "gsdcomo",
                "Ysearcher",
                "sso465",
                "Jsk1957",
                "WalderC",
                "miqrom",
                "OH1702",
                "perenseta",
                "Abomb00",
                "ericjamesu",
                "McTrimm",
                "badgenes",
                "Finderladi",
                "taximadman",
                "tmi",
                "emruddock",
                "gerard",
                "stephenbrad"
            ]
        }
    ]
}