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-180
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Content-Type: application/json
Expires: Wed, 21 Aug 2019 02:52:40 GMT
Vary: Accept

{
    "count": 43,
    "next": null,
    "previous": null,
    "results": [
        {
            "source": "direct-sharing-180",
            "name": "Genetics of Personality Type",
            "usernames": [
                "madprime",
                "gsdcomo",
                "emeadows317",
                "annallull",
                "gedankenstuecke",
                "benc",
                "stgeorge",
                "taximadman",
                "suzannelamonaca",
                "stephenbrad",
                "miqrom",
                "saw2112",
                "laurenshearer",
                "sso465",
                "bradly22",
                "Asuggsnurse",
                "kdgreis",
                "psaglav",
                "furious_rose",
                "acompton6761",
                "swede_male",
                "M_P",
                "dave2019",
                "Laurenshearer86",
                "smallstepstoday",
                "Neat",
                "Robin",
                "Pgtest",
                "zansewek",
                "ricardochavira",
                "bkothe",
                "Suzichains",
                "judao_mandatore",
                "KayPatt",
                "Bauniculla",
                "gordandgabi",
                "maignaci",
                "ComputerCrone",
                "NabilNazir",
                "Ken_Mazer",
                "BigYoshi",
                "SJF",
                "Holofuison1998",
                "bradly4444",
                "Saskins1",
                "rssfed23",
                "TheWarHorse",
                "Karonhia",
                "Katri_V",
                "ptomlinson9460",
                "zstandig",
                "Drj5j",
                "michaljamrich",
                "eishtahalvah",
                "CameoNBlewett12",
                "AlynJohnson90"
            ]
        }
    ]
}