implemented instrument logging
lots of changes

I didn't want to commit before it was error free. I realize now that
this was foolish, because now the changes have snowballed. I basically
completely rewrote the user interface, trying to make the interaction
between the GUI, Instrument, and DataLog more natural. I then started
implementing dynamic adding and removing of plots, as curves were added
or removed... And that still doesn't quite work. I'm going to commit
here, and then try to simplify things down to a point where I can
implement the important features one at a time.