The existing structure didn't make sense, as Sound only handled
sound files, but Music handled both music and short FX decoding.
I've merged Sound & MUsic into a single Sound class, and moved
the music driver to their own file, renamed to SoundDriver
Some strings are still in the base Resources, since they're referred
to by core dialogs. These may be able to be refactored in the future
as support is added for the other games