Support gamescope 3.12.0 and SteamOS 3.5

[Scrumplex]

gamescope 3.12.0 will break vibrantDeck as the properties we have been using so far will be gone.

See ValveSoftware/gamescope@dc60eba

We need to generate 3D LUTs instead.

[Scrumplex]

I got a work-in-progress version at #87

It doesn't have gamma options and the vibrancy slider only supports the "Color Vibrance" values in SteamOS' color settings (see screenshot below)

So for now it's a much less powerful version of the previous vibrantDeck.

It might be possible to increase the range of boosted colors to vibrantDeck 1.x levels by contributing some changes to Valve's gamescope directly. But that would take weeks to months to land in SteamOS anyway

[FlufflessMC]

Would be awesome

[Hedomec]

must have