Shadow excessiveness: Deferred limit reduction

[mcmonkey4eva]

In deferred render mode*, we have easy room to add multiple-pass light additions.
This means we can have theoretically unlimited light sources per frame.
However, we don't currently do that. Why? Efficiency. Achieving higher limits than the built-in is slow.
How can we cheat it in anyway? Multiple runs of the shadow and light-add passes.
One run for each light, or one run each set of lights. Currently we do one run for ALL lights, but we could easily make that add additional passes if the present 'hard' limit is reached.

* Technically we can apply this to forward mode as well, with a slight bit more difficulty...

I think if nothing else it's worth having as an internal option, just in case it comes in handy later.

This will also allow less usage or disabling of the "low quality" shadow map logic (The system by which only 1/4th of the shadow map image is used instead of the whole one to allow room for more) if we choose to enable this feature described above.

#3 is relevant to shadow excessiveness as well.