Tighten up scene graph creation
Tighten up scene graph creation

- Avoid creating dummy vnodes for meshes when possible.
- Rotate cameras to their (correct?) position
- Some slightly tighter docs.
- Some more robustness in realizing vnodes; it would probably be
  possible to use an armature for the whole forest again with minimal
  code changes

ksons/gltf-blender-importer