Fixed Problem regarding negative riTrans values

The reason was a bit sloppy detection of whether the surface normals was
pointing outwards or inwards in a cell.
The cells can be turned inside out due to depth/Z or mapaxis conditions.

ApplicationCode/ReservoirDataModel/RigGridBase.h

@@ -60,7 +60,7 @@ public:
     void                        setGridId(int id) { m_gridId = id; }
     int                         gridId() const { return m_gridId; }
 
-    double                      characteristicIJCellSize();
+    double                      characteristicIJCellSize() const;
 
     std::string                 gridName() const;
     void                        setGridName(const std::string& gridName);