Add Ambient Light effect

[britzl]

With lookup table for ambient light value based on a provided value (time of day 0.0 - 1.0)

Allows things such as "Darker at night, lighter in the daytime. The light’s color set with a gradient. By nightfall a light source not only becomes darker but gets blue tint."

http://www.gamasutra.com/blogs/SvyatoslavCherkasov/20181023/329151/Graveyard_Keeper_How_the_graphics_effects_are_made.php