Merge branch 'matthiaskrgr/light_misc' into 'master'

Matthiaskrgr/light misc

drain: make underground areas a bit darker (was still brighter than post-srgb)

space-elevator: make make a bit darker (reduce skylight) as some players complained; fix sky shaderfile which I accidentally messed up (changed wrong number which moved sun-exit instead of changing sun brightness)

dance: try to increase contrast between dark and bright areas a bit ( @Mario complained)

See merge request !42