Add basic visualization for hdd io.

Presently, on my system, there are about 15 visualizations. In
other words it's monitoring 15 disks and making a really huge
applet.

I'm not sure how to handle what data it should display or have
configurable. Shall I hard-code RIO,WIO into their own colorings and
then the user selects the devices to apply? That would certainly make
things easier for me. At least for now. Ideas welcomed.