Add support for Floaty Hydrometer

[lbussy]

A few people have asked about this. The JSON is as follows:

{
    "floaty": {
        "name": "1",
        "unit_temp": "celsius",
        "unit_grav": "sg",
        "datas": [
            {"time_second":1593521868,"temp":22.4,"grav":1052},
            {"time_second":1593521868,"temp":22.4,"grav":1052}
        ]
    }
}

Because Floaty will currently only work via the Cloud services and phone app, the POST comes from an external system rather than the device posting directly. It is undesirable to have a BrewPi exposed to the Internet, so this is currently on hold pending review by the Floaty author.