Pre-c3b51bc sompyler emits offset.stem_note/motif.stem_note/clause.note
while new sompyler emits line.stem_note/seq.note. Parser now accepts both
parentSlot values for stem_note, motif, and clause children so the app
works against both old and updated sompyler installations.
Also falls back to reading chain.clause directly from stem_note's children
when no stem_note.chain node is present (old format had no chain wrapper).
b56d84befb