Screenshot feature for AR mode

[MrDChristop]

One of the funniest aspects of AR on phones is to take a picture of you loved one or friend with an AR object.

Currently this is not possible in modelviewer since the modelviewer.toBlob() function only captures the 3d canvas so you get a white background in AR mode.

So the only option is to use your phones screen capture. But it would be much more streamlined if we could expose a "Take Screenshot" button in AR mode.

I tried also with the canvas2htlm lib, with no success. I assume for this you would need to get really low on the API level and possibly also combine the camera with the modelviewer canvas.