Chords with stretched fingering for FretBoards and TabVoice

Sometimes chords with a stretched fingering are required. If not otherwise specified the context-property maximumFretStretch is set to 4, though. Resulting in a warning about "No string for pitch ..." and the note is omitted. You may set maximumFretStretch to an approppriate value or explecitely assign string-numbers to all notes of a chord.