Fixing lighting computation for lightkit

Change-Id: Ida65594f7b8581a4fb4cc592245912d518a95f40
Added convenient method to check for gradient opacity

Change-Id: I93fd12cb7d56ecd33f342164c603cefef51fb569
Updated code to use check on availability of gradient opacity

Change-Id: I47246e5d04478eed9c736bac0084bdaf67844312
Removed dead code

Change-Id: I9f95aafe246dbf8646605b36b865983f2ee826a9
Check for two sided lighting

Change-Id: I67b6158732d8267eb7c2aca3c4314ae8ed9fe42d
Commented out debug code

Change-Id: I4015c510cca9448aa4094e8dff9ad3da848b5e47
Renamed for consistency

Change-Id: Ic553edb29b77df743ae63e5a8b80f323d7515dcd
Merge topic 'volume_lighting_and_other_fixes' into master

e4addeb1 Renamed for consistency
c47bd6e9 Commented out debug code
fded3eb1 Check for two sided lighting
258afecf Removed dead code
d50999b9 Updated code to use check on availability of gradient opacity
68efb791 Added convenient method to check for gradient opacity
6c5d0541 Fixing lighting computation for lightkit