teach the scene win to properly build a hierarchy of scene nodes.

cmake_support/OST.cmake

modules/gfx/pymod/export_gfx_node.cc

modules/gfx/src/gfx_node.cc

modules/gfx/src/gfx_node.hh

modules/gfx/tests/CMakeLists.txt

modules/gfx/tests/test_gfx_node.cc

modules/gui/src/scene_win/current_selection_node.cc

modules/gui/src/scene_win/custom_part_node.cc

modules/gui/src/scene_win/entity_node.cc

modules/gui/src/scene_win/entity_part_node.cc

modules/gui/src/scene_win/gfx_scene_node.cc

modules/gui/src/scene_win/label_node.cc

modules/gui/src/scene_win/render_mode_node.cc

modules/gui/src/scene_win/render_modes_node.cc

modules/gui/src/scene_win/scene_win.cc

modules/gui/src/scene_win/scene_win.hh

modules/gui/src/scene_win/scene_win_model.cc

modules/gui/src/scene_win/scene_win_model.hh

modules/gui/src/sequence_viewer/sequence_viewer.cc