This is not really ready for testing yet, there are still a couple of rough edges. Pinning specific nodes works already though (although only in one spreadsheet at a time).
I don't really think that we should display the breadcrumbs like this. It only works when the editor is very wide, and few nested node groups are used. Maybe a shortened version of it can be shown in the header, or it is displayed vertically in a dropdown. That is easy to change later on.
