With this button, you can now move files or directories to any path in
the notebook, including creating new directories (like 'mv -p'). To move
a file, you specify the new destination directory's path.
This achieves the same effect as renaming a file with a new relative
path, but is more clear to users unfamiliar with unix commands --
especially with regard to moving to a parent directory.
Can only move one file at a time currently.