Move scenegraph source to subdirectory scenegraph.
Take PolygonalGeometry out of scenegraph tree. Further devide responsibilities between PolygonalDrawable andPolygonalGeometry.
...
issue #3: Add scene graph iterator and traverser.
Add DrawTraverser.
issue #3: Refactoring.
issue #3: Change DrawTraverser to DrawVisitor.
issue #3: update CMakeLists.
issue #3: Move gl buffer handling from PolygonalDrawable to PolygonalGeometry. Some Refactoring.
issue #3: Add interface for scene graph visitors.
issue #3: ...
issue #3: Attempt to fix a compile error with MSVC.
issue #3: Add break condition to SceneTraverser.
issue #3: ...
issue #3: Delete Iterarator hierarchy. Refacrtor.
issue #3: Use central DataBlockRegistry object for grometry data.
Merge branch 'master' into scenegraph_2

Conflicts:
	apps/cgsee/painter.cpp
	apps/cgsee/painter.h
	libs/core/CMakeLists.txt
	libs/core/objloader.cpp
	libs/core/objloader.h
	libs/core/polygonaldrawable.cpp
	libs/core/polygonalgeometry.cpp
	libs/core/polygonalgeometry.h
Merge branch 'master' into scenegraph_2

Conflicts:
	libs/core/polygonaldrawable.cpp
Merge branch 'master' into scenegraph_2
ref #23 : fixed some syntax errors in class Plane