Pt/return values

[PTheyssen]

This cleans up the runner service a bit and adds functionality for retrieving return values from json response payloads.

The code is not very robust, but the basic idea should be correct.

Currently you can specify a return value that will be extracted from the json response payoads:

With the response json:

   {
          "key1": {
            "key2": 2,
            "key3": [ "look", "what", "we", "have", "done"],
            "key4": {
              "price": 42
            }
          }
        }

and the return value

{
  "key": "arg1",
  "value": "response.payload.key1.key3",
  "type": "array"
}

The providedValues dictionary of a transaction that executes this operation will have the entry {"arg1", "[ "look", "what", "we", "have", "done"]} added after it finishes execution of that operation