Per-scene render settings

[avaer]

This PR allows per-scene render settings using the metaversefile rendersettings type:

{
      "type": "application/rendersettings",
      "content": {
        "fog": {
          "fogType": "exp",
          "args": [[255, 255, 255], 0.01]
        },
        "ssao": {
          "kernelRadius": 16,
          "minDistance": 0.005,
          "maxDistance": 0.1
        },
        "dof": {
          "focus": 3.0,
          "aperture": 0.00002,
          "maxblur": 0.005
        },
        "hdr": {
          "adaptive": true,
          "resolution": 256,
          "adaptionRate": 100,
          "maxLuminance": 10,
          "minLuminance": 0,
          "middleGrey": 3
        },
        "bloom": {
          "strength": 0.2,
          "radius": 0.5,
          "threshold": 0.8
        }
      }
    },

Depends on webaverse/totum#20

[avaer]

We will support limiting the post processing per scene with user-overridable performance settings that guess the spec of the machine that the user is on and guess accordingly.

Something like...

• Low: No effects, just render()
• Medium: Adds shadows
• High: Adds AA
• Supernal: Adds postprocessing

[avaer]

In the future LODs will be changeable this way as well.