Replace SimpleThread by JThread now implementing same features
Directional fog + horizon colors, based on sun & moon positions at sunrise / sunset
Add setting to disable direction dependent fog and sky colors
Remove an unused function and include from client.cpp
Reduce cloud coloring for colored fog and cloud mode
Merge remote-tracking branch 'minetest/master'

Conflicts:
	freeminer.conf.example
	src/defaultsettings.cpp
	src/server.cpp
	src/sky.cpp
	src/sky.h