Polyphonic changes with tests

Rearranged "mergetracks" procedure to classes "Measure" and
"ScoreTrack".
FMotiv: pitch equal check removed to Note.PitchEquals(...) function.
Returned single modulation check.
MusicXmlParser: Chord recognition updated.
Measure: updates to merge measures.
Note: some callback organization, needs review. Added PitchEquals
method.
ScoreTrack: updates to merge tracks.
TestMusicXmlParser: added test of polyphonic parsing.
TestNote1: added test to multinotes equality checking.