removeAll(includesBackground) {
    const canvas = this._canvas;
    const objects = canvas.getObjects().slice();
    canvas.remove(...this._canvas.getObjects());

    if (includesBackground) {
      canvas.clear();
    }

    return objects;
  }
Removes all object or group
@param {boolean} includesBackground - remove the background image or not
@returns {Array} all objects array which is removed