but converting into enum class requires some more work. And mostly for
that reason can't yet get rid of the "KEY_", as it clashes with enum Tpc
(which too hasn't yet been converted into en enum class)
Ambitus elements with accidental(s) are laid out misaligned with ambitus elements without accidental(s).
The new algorithm aligns the leftmost note heads of each ambitus and places accidentals accordingly.
The [undefined] item is informational only (when the ambitus range cannot be calculated, for instance when there are no notes in the staff yet) and should not be selected.
Fixed at two levels:
1) The [undefined] item is disabled and cannot be selected any longer
2) The Ambitus::layout() method is more robust to in dealing with undefined ranges.
