Add custom shader to simulate PS2 behaviours

[Xeeynamo]

This fixes some of the odd texture rendering glitches caused by the inability of emulating the "Texture Wrap Mode" as PlayStation 2 internally does.

BEFORE

AFTER

[Rikux3]

Out of curiosity: What causes these "smudges" in the skybox? I've found them on another map too.

[Xeeynamo]

I think it is a regression caused by the custom VIF interpreter I wrote before merging the engine into master. I am going to confirm later in the day if it is caused by the a regression of this pull request or somewhere else.

[Xeeynamo]

The "smudge" bug is definitively caused by VifUnpacker, which sets the wrong v coordinate to the mesh. I reached this conclusion by verifying the wireframe and comparing (see the screenshot below) before and after this pull request:

I will look into it outside this pull request, since it is not related to the shader I've introduced here.