[BROKEN] interim commit - interleaved plotting on all three axes

A significant amount of work went into getting this far, but
interleaved plotting among the three figures probably doesn't work yet.
Checkpointing changes here before MATLAB eats my .fig file.
Checkpoint commit -- plotting still borked

Plotting works for a single set of axes, but each axes only plots once,
then after that, it doesn't update anymore. The "Clear" button also
only works on the last plotted axes(s) and not any that were previously
plotted on before.
Checkpoint -- just make things simpler from now on

From here on out, hard-code the axis names, use appdata for settings
shared between controls, and other simplifications.
Mostly working. Still some issues with interleaved plots.

Ready for presentation.