Exempt a series in heatmap from color range calculation

[sluedecke]

Summary

Just like
#1843 states, I also want to have a total row in my heatmap. Unfortunately it is included in the color range calculation and thus very 'colored' whilst the cells themselves are only somewhat 'colored'. This is what it looks like:

API Changes

Not exactly sure, but adding a group parameter to the heatmap to group series for colorization or much simpler an noshade option for series.

Intended Use Case

Add a totals line to heatmap which is exempt from shade / colorization computation.