project.newFolder takes optional `items` (ids or names) and moves them into the new folder in
the same undo step, out of any folder they were in; a folder can't go into a new folder made
inside itself. Dropping dragged Project items (the dragged item, or the selection it belongs
to) on the panel's New Folder button runs it, with the drop outline New Composition shows; the
new folder opens with its name ready to type, like one made with the button.
Fixes#3196
vangel76
dd92908bc8