Plot._onDatasetUpdate() name misleading

[aicioara]

protected _onDatasetUpdate() {
  this._updateExtents();
  this._dataChanged = true;
  this.render();
}

Is misleading. Generally methods starting with on are setting a callback, like in

    public onMouseDown(callback: MouseCallback) {
      this._setCallback(this._downCallbacks, callback);
      return this;
    }

While this is clearly a dispatcher.

Method should be deprecated, renamed to _dispatchDatasetUpdate() and removed in v2.0.0