Issue 5635: show new regression-test cases

https://sourceforge.net/p/testlilyissues/issues/5635/

DEMO: http://faithful.be/tmp/test-results/

output-distance.py generates table rows for new test cases, i.e. cases
not present in the baseline.

Score images and profiling results appear in full.

For logs and midi, no diff appears; however, as usual, a link to the
file is provided.

Table cells for missing baseline cases are left empty, and the style
sheet gives these a striped pattern that hopefully hits the sweet
spot of being obvious without being distracting.  Please let me
know what you think.

An improvement would be to add a way to filter out new cases.
I would probably want to revise the way the current filtering works,
so I think it makes sense to leave it all for another time.