add test for belongs_to association with different class name
pass belongs_to User test - very caps sensitive\!
tracks should have many submissions test
pass has many submissions
make track has many submissions test more specific
tracks have stem and remix submissions
update schema pdf after reinstalling graph viz

Used the following line:
brew reinstall graphviz --with-bindings --with-freetype --with-librsvg
 --with-pangocairo
circle have many submissions