Feature Request / Suggestion - Make auto-matte generated layers background layers by default.

A small suggestion, which I think is just a minor fix, would be to automatically set all _Matte layers generated by Auto-matte to background. This way, autofilling one or several layers in one shot doesn’t make onion skin unusable for next/previous shots.

I realize they can be set to background manually, but I thought it’s a minor detail that could be improved.