move JESProgram and JESUI into jes package

This marks the end of all .py files starting with JES. media.py and
colors.py are still outside the jes package, but that's because
they're user API's instead of program internals.
make FileManager absolutize paths

Even though paths were normalized, they could still be saved and
entered into the "Recent Files" menu in relative form.
Now there's an abspath _and_ a normpath.
use quarter/eighth notes in Hot Cross Buns demo

It's been a while since 7th grade chorus.