Support automatically activating or deactivating a VisionMode based on the current darkness level of the Scene

[aaclayton]

User Experience

This would be similar and an alternative to utilizing a scene's globalLightThreshold: a vision or detection mode could enable or disable itself depending on the darkness level of a scene. In this way, globalLight could always be turned off, but tokens representing actors with ordinary human eyeballs could see so long as the "sun" is out. Conversely, it could be a means of implementing a "light blindness" mechanic, to be applied to a subterranean creature that can only see in the dark.

[Feu-Secret]

This feature will not be implemented for v10. We realized that it was not so useful and open to ambiguities. We need to carefuly think about it for v11.