ProcGUI: part way to redoing head based on inverse solution
ProcGUI: improved the contour plot to make more real
ProcGUI: added hooks for rereferencing the montage

Added hooks for rexpressing the EEG data from a single reference
electrode to a whole-head, all-electrode mean as the "reference".  It
turns out that I don't really like how it looks, so I've defeated it.
The code is in-place, though, if I ever want to go back.