NightMode Blockers

In order to be able to publish Night Mode, we have a few things that are minor issues:

# Minimap shadingTex

Minimap shadingTex is not updated frequently enough, and when the lighting changes, then the shadingTex cant really keep up. This results in two different artefacts:

1. when terrain changes force an update, a small area of the shadingTex is updated
2. shadingTex is updated gradually as the lighting changes, so a gradient appears on the shadingTex

shadingTex is calculated based on the heightmap and a really simple 4 color gradient lookup.

## Solution 1

Expose engine uniform buffers to cont/base/springcontent/shaders/GLSL/MiniMapFragProg.glsl
Rewrite shader to calculate the shading from engine uniform buffers and heightmap every frame.

## Solution 2

The engine already updates shadingTex at a regular rate, just slowly. It does it in `for_mt`, allow the toggling of an update manually at a higher rate would be a solution to the gradient and most of the lighting changes problems.

## Solution 3 (best)

Have a shader render-to-texture the shadingTex, instead of using cpu to do so, as all the data required to do this is available in engine uniform buffer.

# Sky rendering does not obey sun changes.

And obviously this doesnt look very good when we try to make it look like night.

`cont/base/springcontent/shaders/GLSL/ModernSkyFS.glsl`

Because it uses
`const vec3 sunColor = vec3(0.992, 0.985, 0.827);`

Could use a lua replacement as well like the infotexture shaders that are semi-customizeable by games.

The semi customizability is actually a little bit limited, because they can only access Spring.GetConfigString stuff.

# Skybox cannot be darkened easily

`cont/base/springcontent/shaders/GLSL/CubeMapFS.glsl`

Could use a lua replacement as well like the infotexture shaders that are semi-customizeable by games.

# Bumpwater shader issues

I now forget what these were, outside of the shores being too light and not affected enough by sun changes.