enable PBR for lightMapping rendering and add support for physicalMap

[illwieckz]

This PR sits above #230.

Enable PBR for lightMapping rendering, add support for physicalMap.

physicalMap expects ORM support (glTF 2.0 standard).

Test map provided by @SomaZ, I edited the shader, converted the assets and build the package the way this branch expects it:
https://dl.illwieckz.net/b/daemon/wip/pbr/map-test-pbr_0%2B20191212-075241%2B9a1edb3.dpk

I removed the swizzle mask code because as long as we don't get expected result on PBR side, we can't know if experiments with swizzles are working or not.

The PR introduces r_physicalMapping cvar, which is currently disabled by default (set to 0) since PBR is not production ready.

Some part of the PBR rendering looks OK, but the lighting is not. Fixing PBR is out of topic. This PR is about being sure assets are piped through the engine from VFS to GLSL. It would make debugging PBR far easier.

[illwieckz]

I removed the swizzle mask code because as long as we don't get expected result on PBR side, we can't know if experiments with swizzles are working or not. The textures from test map were converted to not require such feature.

[illwieckz]

This PR is no longer WIP because remaining PBR bugs seems related to the implementation itself, not to the proposed changes made to enable it.

[illwieckz]

I noticed the PBR compute is not done when there is no normalmap. That's something to keep in mind but that must not prevent the merge of this PR. This PR is there to make life easier to people wanting to work on the PBR part of the engine (which looks incomplete). A GLSL wizard would then just have to focus on fixing/completing GLSL code since PBR maps will be loaded right.

[illwieckz]

This now looks ready to me. I have more revamp ideas but that would be another PR. Let's do it step by step.

[illwieckz]

I renamed materialMap to physicalMap, the material word was too much generic and was a creation introduced in e85abec (“Support materialMaps (PBS).”) and never used yet. So there is no problem to set a better name instead.

[illwieckz]

rebased on master

[slipher]

looks OK

[illwieckz]

I just added a commit to properly route through PBR mapping if r_physicalMapping is enabled and shader is physical or, if it's not a physical map and r_specularMapping is disabled or it's not a physical map but r_specularMapping is disabled, produce something. We need to test everything…

r_physicalMapping is still disabled by default.