Should add ondelete=cascade on menuitems

hello,

when deleting a menuitem, the current behavior is to do nothing for children of this menuitem: it means that they will appears at the left of the screen (under partners, e.g) because they now have parent_id field = False.

I suggest to
*either, add ondelete='cascade' in order to delete the menuitem + all its children and recursively
*either, link all the children to the parent of the deleted menuitem

Both seems to me more logical than current behavior but i have a preference for the first one (ondelete=cascade) because i think it is what people want to do most frequently.

Thanks