#2822, #2731, #2730 Rewrote the legend layout completely.

Now using preferred size unless it is higher than 0.7 viewer height.
If higher,  then use viewer height.
Stacks legend in columns not higher then the viewer.
Update layout on resize without triggering recreation of legends.
Place axiscross in right bottom corner.

ApplicationCode/UserInterface/RiuViewer.h

@@ -127,6 +127,7 @@ protected:
     virtual void    leaveEvent(QEvent *) override;
 
 private:
+    void            updateLegendLayout();
     void            updateTextAndTickMarkColorForOverlayItems();
     void            updateLegendTextAndTickMarkColor(cvf::OverlayItem* legend);