UFO:Alien Invasion Code

* crushed png files

* Recompressed all textures in base/textures/tex_material with Trimage image compressor and commited those files, where a filesize reduction of at least 5% (up to 92.3%) was achieved

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

* Adjustments to tex_material/metal012 and 013

* Some new textures, still need work

* Some flat, tileable concrete and metal textures