get strip chart mode working again by putting back in some of the code to process the old SignalLines
allow us to "mute" the first channel and still see Lissajous curves on the second
remove code that's been commented out for over 20 years
in accumulate mode, limit the number of old traces to ten, and fade out their color
don't rescale/reshift the saved signallines; makes it easier, so we don't recompute them anymore
a working x-y display
my first attempt at a crude x-y display
configure changes suggested by "autoupdate"