function getCanvasSize (canvasEl, embedded) {
  if (embedded) {
    return {
      height: canvasEl.parentElement.offsetHeight,
      width: canvasEl.parentElement.offsetWidth
    };
  }
  return {
    height: window.innerHeight,
    width: window.innerWidth
  };
}
Return the canvas size where the scene will be rendered
It will be always the window size except when the scene
is embedded. The parent size will be returned in that case

@param {object} canvasEl - the canvas element
@param {boolean} embedded - Is the scene embedded?