[DRAFT] Skybox experiment

[NeylMahfouf2608]

Two examples of skybox implementation :

• first one is based on a huge cube mesh which renders textures on backfaces (i.e to the interior). It opens many possible customisation (animation, special effect with custom shader...) , but requires a large mesh, six materials, and can cause other problems (especially with shadows)

• second one uses the background propriety of three.Scene object. It is faster and easier to use. It is also less dangerous. It has less customisation possible natively. But it can be used as "environment texture" for shiny meshes in the scene that will reflect it, like metals.

THIS DEMO USES ABSOLUTE PATHES FOR TEXTURE - You will have to modify it in order to test it