moveTo(Object, index) does not trigger history:append

[cyruscuenca]

I've implemented a layer control feature with fabricJS. I also implemented fabric-history for the canvas. When switching layers with moveTo, there aren't any fired events. I think layer changes are pretty major events, and should probably be "undo-able".

Steps to reproduce:

1. Create an fabricJS canvas
2. Add fabric-history
3. Add a few elements
4. run moveTo on an object

And you won't be able to undo the layer change