* support for SSI container format - this is an obscure format used by a few Duke Nukem mods - added to have this subsystem identical between both engines.
* removed some dead wrapper code
* made the Open methods local to their implementations, this was never called virtually.
* handle brightmaps in the main shader instead of keeping separate instances around.
* added detail and glow layers from Raze.
* fixed material setup which could not guarantee that everything was initialized correctly.
* for warped textures, warp all layers. With this brightmaps finally work on warped textures.
Note: Vulkan reports a "device lost" error with this which still needs to be investigated.
