Ticket originally opened by Neil Mather on old QPsycle's bug tracker.
When closing a song, qpsycle should check if changes have been made to the present song, and if so, prompt the user to save them. This requires a method of registering changes to the song.
Possible places to look for ideas are at the Psycle source code, and also at the Qt Undo Framework (though this will involve writing some kind of Qt wrapper to the psycore song file -- Qt code should not go into psycore.)
More generally, we need Undo-Redo features.
(Then checking whether the song was modified when closing it can simply be done by checking whether the Undo stack is empty)
