code: function startActivity (activityId) {
    var timestamp = new Date().getTime()
    var body = 'activityId=' + activityId + ':timestamp=' + timestamp
  
    return this.request('startactivity', body, 'encoded', function (stanza) {
      // This canHandleStanzaFn waits for a stanza that confirms starting the activity.
      var event = stanza.getChild('event')
      var canHandleStanza = false
  
      if (event && event.attr('type') === 'connect.stateDigest?notify') {
        var digest = JSON.parse(event.getText())
        if (activityId === '-1' && digest.activityId === activityId && digest.activityStatus === 0) {
          canHandleStanza = true
        } else if (activityId !== '-1' && digest.activityId === activityId && digest.activityStatus === 2) {
          canHandleStanza = true
        }
      }
      return canHandleStanza
    })
  }
docs: Starts an activity with the given id.
  
  @param activityId
  @returns {Q.Promise}