Change transfer format

[lexaux]

Please see issue lexaux/RoadworksSensorLogger#16 in the client app - the data which runs between client and server changes, so we'll need to adapt to it.

[lexaux]

The new upload (POST) format is the following:

[
    // single record object
    {
        // CSV-style data of the session. Heading shows its structure pretty well.
        "data": "Time, Severity, Lat, Lon, Speed\n1392495160711,27.623926877975464,0.0,0.0,0.0\n",

        // session start time and end time
        "startTime": "Sat, 15 Feb 2014 10:12:39 EET",
        "endTime": "Sat, 15 Feb 2014 10:12:41 EET",

        // client-side ID of the session
        "id": 23,

        // amount of events logged. This is the amount of lines in 'data' field (remember the heading)
        "eventsLogged": 1
    }
]

[ImmortalJoker]

does it necessary store to "data" strings as first line?