Proper baked/precomputed occlusion

Please add support for proper baked/precomputed occlusion information. Either using umbra or whatever in-house solution is available.

Currently available built-in occlusion baking appears to be pretty much 2 dimensional - meaning it generates nearly 2d grid of cells with specified height. Meaning that in levels with verticality the data will be useless.

The reason why I’m requesting this feature is because currently available mechanism generates flickering unless whoever created the level also makes low-poly “filler” meshes for every wall. Given thatBSP hasn’t been updated for a while, this is very strange, because BSP would be a primary tool for making those fillers.

Either way precomputed occlusion would be quite useful, since minor extra memory overhead is a small price to pay.