#3941 Improve contour map performance by several measures

* Discarding triangles that aren't inside current level. Big gain.
* Checking bbox for contour levels. Minor gain.
* Doing less interpolation. Minor gain.

ApplicationCode/ProjectDataModel/RimContourMapProjection.h

@@ -50,6 +50,7 @@ public:
     {
         std::vector<cvf::Vec3d> vertices;
         double value;
+        cvf::BoundingBox bbox;
     };
 
     enum ResultAggregationEnum