Fix compare by time / by distance bug

.. silly typo mean't allplot was being used as a refrence
   when generating plots instead of fullplot

.. this manifests itself as using the wrong plot for the
   'bydist' boolean -- this is fine, unless you switch
   between by time and by distance whilst in compare mode.
UI Nits: Colorblind

.. tweaked color sequencing in compare to avoid using
   red/green as it should be avoided -- red/green color
   blindness is relatively common.

.. this is just a hack in the absence of a good algorithm
   to generate distinct hues automatically.
Fix Ride plot zone shading for series stack

.. the setting wasn't being set/unset according to
   user preferences properly.
AllPlot Paint Zones in Compare Mode

.. we should actually paint a zoned background if
   power shade zones is selected, when in compare mode.

.. but /only/ for charts that have power on them!
Hide empty series plots in compare mode

.. check the curves are empty!
merge upstream into master