Voxel-level ambient occlusion optimization bits generation via compute shader

• Test scene: nuke.vox (1932x615x1136 or 31,734,800 non-air voxels)
  • Times from/to on scene load to generate voxel-level AO optimization bits:
    • CPU (only using one execution thread @ 3.20GHz) : 134 seconds
    • GPU via compute shader: 2 seconds

[Updating of voxel-level AO optimization bits when blocks/voxels are placed or removed has a bug that needs fixing.]