GET on Device/Transducer should return one value by default

[linux4life798]

The GET on a transducer should return a very fast last value by default that is plain text.
When a limit is specified, then it can return influxdb data.

[linux4life798]

The GET should be the opposite of the POST.

Currently, you can POST with plain/text and just place the value in the body. Doing a simple GET on the with plain/text on the transducer should yield that same simple last value.

This can then be augmented to allow the limit parameter to grab lots of values.

[hi-liang]

Is timestamp important on this last-value return?

Current behavior of data from Influx returns something like:

{
  "results": [
    {
      "statement_id": 0,
      "series": [
        {
          "name": "5979209b2d16735bdcadecdf_cloudiness_percentage",
          "columns": [
            "time",
            "value"
          ],
          "values": [
            [
              "2017-07-26T23:10:00Z",
              1
            ]
          ]
        }
      ]
    }
  ]
}

Most basic return then might be { value: 1, timestamp: "2017-07-26T23:10:00Z" }

[linux4life798]

I was thinking that it is the mirror image of the POST, but that would not have a timestamp.