There's several JS drag-and-drop ordering libaries mentioned here: http://stackoverflow.com/questions/10361779/drag-and-drop-to-reorder-html-lists
Searching for "javascript order by dragging jquery" turns up some additional hits. (It'd be preferable to use something based on jQuery, because that's already in wide use in Mahara.)
There's several JS drag-and-drop ordering libaries mentioned here: http:// stackoverflow. com/questions/ 10361779/ drag-and- drop-to- reorder- html-lists
Searching for "javascript order by dragging jquery" turns up some additional hits. (It'd be preferable to use something based on jQuery, because that's already in wide use in Mahara.)