Validate weather/env-effects (rain, clouds, haze, etc.)

[kb173]

Four factors need to be taken into account in a more unified model:

1. Cloud coverage
2. Cloud density (+ lightning strikes?)
3. Haze
4. Lighting (directional vs ambient)
5. Rain (amount & size)

[kb173]

We should test our implementation against reference images, e.g. a webcam like this: https://www.bergfex.at/sommer/wienerwald/webcams/c20882/