Add a subfolder for models and transfer models from server to client

Add a subfolder for models and transfer models from server to client

(obj, md2 and md3 are currently allowed)

Get rid of the texture string and use the existing textures array. Segmented meshes have multiple materials, and this will allow us to texture each. Do not switch to this commit yet!

If a texture string is left empty in LUA, don't modify that material. Useful so a script can change specific textures without affecting others