Reorder menu items capability

Issue Summary

At the moment it is apparently impossible to reorder menu items (by changing their weights). Would it be possible to have:

1. "up" and "down" buttons that allow you just to move menu items up and down the list (equivalent of changing weights)
2. "in" and "out" buttons that allow you to promote and demote menu items (ie make them children or parents of other menu items

Both these functions should work on the page without forcing you to go back and forth to the server - then be fixed like everything else when you press the "Submit changes" button.