Gray-out save menu option and diskette icon when no pending changes

[On reflection, the asterisk on the score tab is probably sufficient visual feedback. I am closing this issue.] There is currently no visual feedback to confirm that a save action has completed. When using MS on a tablet, it is not always clear whether tapping the save icon actually 'took' due to the uncertainty of finger-taps. It would be helpful if the save actions were only enabled when there are pending unsaved changes. This would be consistent with the behavior of many familiar tools, and would avoid worrying about losing work.