(#80) Fix for CAD navigation mode

Made sure that left mouse button + drag is panning. The view is still
picked when clicking the left mouse button, unless there have been mouse
moves/navigations that led to redrawing of the view.

ApplicationCode/UserInterface/RiuCadNavigation.h

@@ -43,4 +43,5 @@ protected:
     bool            m_isRotCenterInitialized; 
     bool            m_isRotating;
     cvf::Vec3d      m_pointOfInterest;
+    bool            m_navigationUpdated;
 };