Add reverse translator for "convert" task

[dzwillia]

The Contact Refinement example uses the convert() task. It appears the task is working, however, there is no reverse translation of the task JSON back in the JS SDK command; instead the task appears as follows:

  .task({
    "eid": "cc13wmt2jfhz",
    "params": {
      "columns": [
        "givenname",
        "surname",
        "streetaddress",
        "city"
      ],
      "operations": [
        {
          "operation": "case",
          "case": "upper"
        }
      ]
    },
    "op": "transform"
  })