GS - add note to Staff + Music.js

-Music.js (moved Note prototype + static music functions)

-changed "note.getSprite()" to static "getNoteSprite()"
-getNoteSprite() takes a ratio

-gs.processInput()->gs.onMouseDown()->gs.addNote()
-gs.addNote() / staff.addNote()
-noteGraphic placed on staff (correct location)
-note is played!