Do not render on every add/remove
Do not render on every add/remove

On Node, calling `fabric.add` and `fabric.remove` will trigger a
rerender. This fails hard, as we do not have `requestAnimationFrame`
available on Node to schedule a rerender. This flag to the Canvas ctor
allows disabling the automatic update. We manually call `renderAll`
before writing out the processed images.

See: http://fabricjs.com/docs/fabric.Canvas.html#renderOnAddRemove

iFixit/node-markup,iFixit/node-markup,iFixit/node-markup