Limit palette for a Heatmap color

.. hue goes red-yellow-green-cyan-blue-magenta-purple-red

   we only really want the first half of that range for our
   heatmap, which effectively makes it red-amber-green with
   cyan for very low numbers.

   As a palette it will make a lot more sense to the majority
   of users.

   We may look to add multiple schemes, for example limit to
   a single color range or brown/blue etc etc.

src/Core/Utils.cpp

@@ -600,7 +600,7 @@ QColor
 heatcolor(double value)
 {
     QColor returning;
-    returning.setHslF(1-value, 1, 0.5f);
+    returning.setHslF((1-value)/2, 1, 0.5f); // hue goes red-yellow-green-cyan then blue-magenta-purple-red - we want the first half
 
     return returning;
 }