add graphing

Submitted by Richard Tatyr

Assigned to Xfce-Goodies Maintainers

Please implement graphing, much like the CPU load plugin.

Scaling the graph to cube root (or something similar) is useful because linear scales don't show much at such small sizes.

I also like to see two parallel streams (up/down) which can be arranged vertically if resolution is more important than time.

This GPL software (OS X) seems to be a good compromise; it's simple and delivers essential utility while avoiding unnecessary complexity/clutter.