A3DGE Code

* Octre improved: constructor uses default values and added a method to change
octree properties.
* several refactorization on TWorld3D making it more coherent and more easy to
use and maintain, modifying behaviors and adding some methods and properties.
- Added a new example to test the TWorld3D class.
* Small fixes in a3dge.PLG and a3dge.Skybox.
* A small improvement in objviewer tool.
- Removed several "inline" stuff.