This adds some extra options to disable certain rendering features, such as image maps, lights, shadows,
atmosphere, bump maps, etc. Intended to be used for diagnosing rendering problems.
"Inspired" by Arnold.
Cycles: More work on feature overrides
Cycles: Removed some of the unused feature overrides
Cycles: Implemented feature overrides for split kernel
Cycles: Renamed "ignore Atmosphere" to "ignore Volumes"