fix layout issues with offset chords & notes

Once again, fixing one issue led me to discover and fix a few other inter-related ones.  These all have to do with the calculation of the space to the left and right of a segment, which in turn depends on space to left and right of a chord, which in turn depends on the placement of accidentals and grace notes.  Each of these calculations was off in some way with respect to chords or notes with a user offset applied.  Some of the grace note calculations were off even for chords with no user offset.

I won't swear it's all perfect now, but the layout behavior when moving a chord or note (user offset) should be more logical than before (either previous developments builds or 1.3), and grace note layout is improved overall.