Cook-Torrance BRDF, Motion Blur, Lens Flare and more!

Implemented Cook-Torrance BRDF shading model with two normal distribution functions: GGX and Beckmann. This comes with new textures which determine material type (dielectric/metallic) and roughness.
Implemented motion blur effect, consistent with frame time.
Implemented lens flare effect.
Camera animation (no collisions, currently).
Artist parameters (changeable on-the-fly) are now exposed to the user via the HUD. Use the arrow keys to modify them in real time.
Resources are now loaded on separate threads, drastically reducing loading times. The progress, along with thread IDs, is shown in the console.
Some tuning to bloom, DoF autofocus time, shadow map rendering, RSM.
Rendering will be paused when window is out of focus, giving other applications more CPU time.
Bokeh DoF effect is now disabled by default due to it being very expensive. Can still be enabled via HUD.