[Denemo-devel] Enabled deleting menu items.

[Richard Shann]

I've checked in code to enable users to delete menu items (scripts only,
built-ins can only be hidden). As with "hidden" menu items the interface
is in the command management dialog.
This will prevent users' commandsets getting bloated with every script
they have ever loaded, and avoid name clashes of new scripts with old
unwanted ones.
Richard