Stop rendering the graph after process completes

After the process completes, the graph code will proceed to loop around
and print a cooled down oven line. This doesn't look good. Added option
to stop rendering the graph as soon as we hit the Completed step.

NOTE: This version will stop rendering everything, including
temperature. A future version will render the current temperature when
done.
Continue updating temp when not updating graph

Shows current oven temperature after Complete phase, which is what it
should have done after my last change.