Re-shape the tracking data

[nigini]

Based on initial experimentation, the tracking data does not play well with our data export functionality:

A likely better shape would be:

tracking : {
  $tracking_type: {
    $location: {
      $order: { //will help to avoid overlap when the data is flattened 
        $data1: ???
        $data2: ???
     }
  }
}

With the exception of tracking, all the other fields are the value of the named data point.