Added osg::CullSettings class as a way of collecting all the various

settings related to the cull traversal in one place, so we can keep APIs
for settings these values more consistent.

src/osg/CullStack.cpp

@@ -17,9 +17,6 @@ using namespace osg;
 
 CullStack::CullStack()
 {
-    _cullingMode = DEFAULT_CULLING;
-    _LODScale = 1.0f;
-    _smallFeatureCullingPixelSize = 2.0f;
     _frustumVolume=-1.0f;
     _bbCornerNear = 0;
     _bbCornerFar = 7;