Added mp3 file with blank id3 tag. models.Track was not working on files that
would otherwise be compatible, but have blank tags. Added a fixture in the new
pytest format to test_Track.py that provides the untagged file's temporary
path.
My untagged file was indeed not tagged. Fixed that. Added test that fails
properly on reading the untagged track. Time to fix.
Fixed issue where files with empty tags were not opened by Track.
Minor change to ease importing in interactive use.