Use static background name.
Change style code for save space and improve readability.
Now not declare variables, use the value call inside 'println'.
Unified Glossy and Coated Glossy Material UI definitions.
Only one or two parameters are different.
Unified Glass and Rough Glass Material UI definitions.
Same case of glossy..
Change most general 'Type' variable name for more specific "LightType" name.
Remove Background UI code from Light types UI.
Star code for add Background settings to Render panel UI.
Delete very old, unused and deprecated vertex color code.
Delete unused 'hard' value in materials
Improve style code.
Improve some DEF values:
    FG samples 100 -> 16
    Caustic depth 10 -> 5
    SSS photons 1000 -> 10000
Change some float types to integer.