C++ GLTF to Metal backend

Try to use C++ bindings to Metal Objective-C interface.
Render GLTF models with basic PBR direct lighting.

Roadmap:

• [X] PBR direct lightning
• [ ] IBL lightning
• [ ] GLTF Extensions
• [ ] Test models validation
• [ ] Camera controls
• [ ] API public interface
• [ ] Screen passes

Github