[plt-scheme] Handbells for the 21st Century

The notes are pre-loaded.  As for the rest, you're right on.  It tests
three things:

- ability to detect motion
- ability to play a note using effects
- our JavaScript/HTML/CSS i/o interface (for selecting the note)

Our style of combining effects with World is similar but not identical
to Matthias's style in Universe.

But ultimately, yes, that's what it is: detect motion, play note.

Shriram