Ignore Unpitched objects in key analysis

[jacobtylerwalls]

Fixes #1525

[coveralls]

Coverage: 93.072% (-0.0007%) from 93.073% when pulling dd1b7fb on ignore-unpitched-key-analysis into e45753d on master.

[mscuthbert]

We should be able to replace this:

        for n in streamObj.notes:
            length = n.quarterLength
             if n.isChord:
                 for m in n.pitchClasses:
                     pcDist[m] += length
             elif isinstance(n, percussion.PercussionChord):
                 for m in n.notes:
                     if isinstance(m, note.Note):
                         pcDist[m.pitch.pitchClass] += length
             else:
                 pcDist[n.pitch.pitchClass] += length

with:

        for n in streamObj.notes:
            length = n.quarterLength
            for p in n.pitches:
                  pcDist[p.pitchClass] += length

[jacobtylerwalls]

Unfortunately, I see this (and having a vague memory of running into this while dev'ing, should have called it out):

Shall I fix this first in a separate PR? EDIT: done! in #1547

>>> from music21 import percussion, note
>>> pChord = percussion.PercussionChord([
...     note.Unpitched(),
...     note.Note('E-4'),
...     note.Note('B-4'),
... ])
>>> pChord.notes
(<music21.note.Unpitched object at 0x10d793850>, <music21.note.Note E->, <music21.note.Note B->)
>>> pChord.pitches
()

[mscuthbert]

THANKS!