Ssgi

[e2002e]

This pull request introduces changes to the rtao shader and reimplements rtgi from version 19.02. Changes are:

• no tweak to ssgiRayStep value
• base distance factor of 1.0
• maxSteps option is remove in favor of step & search dist which are used to compute the maxStep like in ssr.
• no changes are made to fragColor during rayCasting, we store the final value in a variable and will afterward assign to fragColor and divide / multiply according to the number of cones.
• rtgi uses another blur shader because the rtao / ssao one just work on one channel (I retrieved the old code's shader).
• rtgi uses it's own render target (RGBA32).

[e2002e]

I need to rework the rtgi.