code: function (key, handler, obj) {
              var property = this.config[key.toLowerCase()];
              if (property && property.event) {
                  return property.event.unsubscribe(handler, obj);
              } else {
                  return false;
              }
          }
docs: Unsubscribes an external handler from the change event for any
  given property.
  @method unsubscribeFromConfigEvent
  @param {String} key The property name
  @param {Function} handler The handler function to use subscribe to
  the property's event
  @param {Object} obj The Object to use for scoping the event
  handler (see CustomEvent documentation)
  @return {Boolean} True, if the unsubscription was successful,
  otherwise false.