Make additional changes to the new version of musicxml2ly (issue 297370043 by address@hidden)

[john]

Reviewers: ,

Message:
A few days a go I uploaded a new patch for issue 4751, "Import
Philolelos enhancements to musicxml2ly", the first patch for which had
been flagged as needing work. I hope this version works better.

Description:
Make additional changes to the new version of musicxml2ly imported
from the Philomelos project. The changes are also uploaded to the
branch dev/johngourlay/issue-4751. After these changes I can run the
following build commands without error:

make
make test-clean
make test
make check

The problems with the earlier patch were due to my misunderstanding of
the make test dependencies. I did not run make test-clean, and so I did
not see that some musicxml regression tests did not run.

Please review this at https://codereview.appspot.com/297370043/

Affected files (+3760, -2169 lines):
  M python/musicexp.py
  M python/musicxml.py
  A python/musicxml2ly_conversion.py
  A python/utilities.py
  M scripts/musicxml2ly.py