Fixup Stack By Series

Finish off the nits and missing pieces for the recent
update to enable plotting in a stack by data series;

* Now plots W' bal, LR Balance and headwind
* Stacks are now redrawn when settings change
* Interval marking is fixed
* Baseline is now set correctly for each plot
* Reference lines are plotted (on power plots only)
* Reference lines can be dragged
* Interval markers are not redrawn with the text
  only shown on first plot