Unify the width of all visible legends.

* Calculate the minimum width to fit the content before the render pass.
  * Set the actual width of all the legends to the largest of the minimum widths.
  * This resizes the legends to always be the same size and reduces the size of you remove
     the widest legend.

ApplicationCode/ModelVisualization/RivTernarySaturationOverlayItem.h

@@ -41,6 +41,7 @@ class RivTernarySaturationOverlayItem : public caf::TitledOverlayFrame
 public:
     explicit RivTernarySaturationOverlayItem(cvf::Font* font);
     ~RivTernarySaturationOverlayItem();
+    virtual void    computeLayoutAndExtents() override;
 
     void setRangeText(const cvf::String& soilRange, const cvf::String& sgasRange, const cvf::String& swatRange);