Split deferred shading pass into multiple draw calls, one for each light

[RiscadoA]

Solution

Each light = one screen quad draw call, with additive blending enabled.

[RiscadoA]

We're unsure on whether this would speed up stuff or not. We should experiment and measure the results, along with #211.

[RiscadoA]

What's the status of this @tomas7770?

[RiscadoA]

I'll set it as urgent as this should allow some interesting optimizations such as light volume culling (#1180)

[tomas7770]

What's the status of this @tomas7770?

Nothing has been done yet.