Return JSON result format for EC and fluoride tests

[mtwestra]

The EC and fluoride test need to return the JSON result format described in https://github.com/akvo/akvo-flow/issues/1577#issuecomment-179288000

[nhternup]

For review: The JSON result for EC Sensor looks like this for now

{
    "device": {
        "product": "2014818",
        "os": "Android - 4.4.4 (19)",
        "model": "2014818",
        "language": "en",
        "manufacturer": "Xiaomi",
        "country": "US"
    },
    "testDate": "2016-07-04 14:09",
    "app": {
        "appVersion": "0.110 Beta",
        "prefLanguage": "fr",
        "language": "en"
    },
    "result": [
        {
            "value": "21286",
            "id": 1,
            "unit": "μS/cm",
            "name": "Electrical Conductivity"
        },
        {
            "value": "29.6",
            "id": 2,
            "unit": "°Celsius",
            "name": "Temperature"
        }
    ],
    "uuid": "[f88237b7-be3d-4fac-bbee-ab328eefcd14]",
    "type": "caddisfly",
    "name": "Electrical Conductivity"
}

[nhternup]

{
    "type": "caddisfly",
    "name": "Nitrate - N & Nitrite - N",
    "uuid": "c801b70c-39e4-493a-b20e-6843158b47b4",
    "result": [{
        "name": "Nitrate Nitrogen",
        "unit": "ppm",
        "id": 1,
        "value": ""
    }, {
        "name": "Nitrite Nitrogen",
        "unit": "ppm",
        "id": 2,
        "value": "0.86"
    }],
    "image": "bac35468-4217-421c-886f-3e89e386b403.png",
    "testDate": "2017-01-11 08:47",
    "user": {
        "backDropDetection": false,
        "language": "en"
    },
    "app": {
        "appVersion": "Version 1.0.0 Alpha 7.2",
        "language": "en"
    },
    "device": {
        "model": "SM-J500F",
        "product": "j5ltexx",
        "manufacturer": "samsung",
        "os": "Android - 6.0.1 (23)",
        "country": "GB",
        "language": "en"
    }
}