Minor Fix

Corrected issue where chk_all_voice_combos was written as
chk__all_voice_combos thanks to careless use of auto-replace.
Revised ChordNGram str()-making Algorithm

I moved the fixed strings into class variables, and changed "is" to
"ident," as requested by Prof. Rusch.
List of Parts Displays in "Analyzing" Panel

Previously, the "analyzing" panel didn't correctly display the list of
parts in a piece. Now it does.