Create new groups in File3dm

[cedemax]

It seems that there is no way to add groups/group objects when creating a new File3DM object. This would be very useful, as groups are a great feature. Is there a reason why groups cannot be created?

There are methods on ObjectAttributes to add to groups and remove from groups, but these don't seem to create new groups?

[sbaer]

I looks like we need to expose some additional Add routines to the GroupTable on File3dm

[fraguada]

fyi, this already works in js and py

[fraguada]

We will need to add a way to create a group object outside of Rhino SDK.

[fraguada]

This has been added via https://github.com/mcneel/rhino3dm/pull/574