Global lighting

We need global lighting(lighting affecting the whole map) to simulate things like time of day.

It should simulate a very distant light source orbiting around the map
(e.g. Sun or Moon "orbiting" the Earth).

It _might_ change its color based on the time day (e.g. member to Sun- duskDawnColor)

There should be up to 8 global lights
(due to OpenGL 1.x limitations - and - eight suns should be enough for everyone).

This will require quite a few changes:

class Light:
public virtual setColor(RGBA8 &)=0;
//no reason to be private?
public f32 intensity;
etc.

class GlobalLight : public Light
//can be changed to a quartenion or anything else
private Vector3 direction
//outside classes always communicate through vectors
public setDirection(Vector3 &)

class Sun
private GlobalLight* light
//period of orbit in seconds
public f32 period
//axis of orbit - could be quaternion or whatever
private Vector3 axis
public setAxis(Vector3 &)
//does stuff to keep direction of the light in line with time
public update()
etc.

Driver specific internals:
class GLGlobalLight: public GlobalLight
//can be any color format for implementation, e.g. RGB565
private RGBAf32 color;
public setColor(RGBA8 &)

Changes in VideoDriver interface:
createGlobalLight(RGBA8 &)
deleteGlobalLight(RGBA8 &)

Other changes needed:
level 1: All surfaces need a single simple normal value, that'd be the normal of a basic flat tile
This'd have an effect similar or identical to an ambient light.

level 2: Tiles should have normal values per vertex.
Basically, a whole tile would have a single normal that'd be identical for all its vertices,
for now. This will require modification of data used to draw in immediate mode, vertex arrays
mode as well as VBO mode.

level 3: Tiles would have simple normal maps. Needs multitexturing.

level 4: Other surfaces (units) would have normal maps- complete 3D lighting

Implementation notes:
SW driver can only implement level 1 (with a sane mind), and maybe shouldn't do it at all.
OpenGL fixed function mode has to use OpenGL builtin lights (limited to 8)
OpenGL shader mode has to use shader based lights.