Add the ability to add an empty scene node to the scene in the scene editor.
Improve some of the rules with scripting.

The new changes reduce the flexibility of the scripts, but greatly simplifies the code.
Add early support for showing a GUI via scene node scripts.
Add support for changing the friction of a dynamics component in the scene editor.
Add support for changing the restitution of a dynamics component in the scene editor.
Fix a bug where a model component was not marking itself as modified when a material was changed.
Cleanup.
A few tweaks to the renderer.

- Gaussian blurred point light shadows (not spot lights yet).
- HDR clamping.
- Fix for refractive transparency.
Add shadow blurring to directional and spot lights.
Fix a bug where meshes with a negative scale were not having their winding reversed upon importing.
Fix a bug where sometimes the first face of a point light shadow cube map is not getting drawn correctly.
Reduce the size of point light shadow maps for now.