UFO:Alien Invasion Code

* base/textures png crush.

* Recompressed all textures in base/textures/tex_buildings with Trimage image compressor and commited those files, where a filesize reduction of at least 5% (up to 95.2%) was achieved

* Reduced filesize of the tex_buildings textures folder by compressing/optimizing the .png files with pngout

* Texture adjustments

* Some new/updated textures

* Committing the wall_grunge textures