Render Darkvision as Greyscale

[aaclayton]

https://discordapp.com/channels/170995199584108546/517504137403826177/517513141551366165

Have a “toggle grayscale” for the player vision, so it can better represent Darkvision (D&D). Ideally, though, players with Darkvision enabled would have a separate vision circle for dim and dark parts of the map.

[aaclayton]

This is a huge and difficult problem, but a very frequently requested feature.

[kjolern]

Could this be closed due to the release of version 10 ? https://foundryvtt.com/releases/10.283.
@arbron @aaclayton

[aaclayton]

I think we can close this in favor of the issue #1166 that was opened.