Support scale-only animations in the model converter

Should be merged upstream to glTF
Clean up variable name
adding support for meshes without a material
cleaning up animations: animation flattener exports matrices too now.
move Open3DGC related code to extensions
remove dead code
fix optional o3dgc file support in cmake
integrate latest o3dgc updates
first cut on compressing animations
experiment https://github.com/KhronosGroup/glTF/issues/141
compressed animations++
wrapping up o3dgc compression
TIME goes through same code path, so that he can be compressed.
update models to reflect latest converter changes
fix crasher and implement close on output stream
update assets to latest version