Add possibility to specify non-translated texts in GUI XML files, and use it for debug strings that should not be translated
Update strings
Cleanup additive material detection
Fix split_stream wrong blending op

"immediate_draw" objects were assumed to be always blended but
splitstream is additive.
Message dialog: set buttons text before layout occurs, so that buttons get the proper size. Fixes #1764
Use deferred shading instead of light prepass
Implement DFG LUT for phong specular
Use GGX D + Schlick G for BSDF and burley for Diffuse