JVET-M0883: Using regular merge index signaling for triangle mode

source/Lib/CommonLib/Rom.cpp

source/Lib/CommonLib/Rom.h

source/Lib/CommonLib/TypeDef.h

source/Lib/CommonLib/Unit.cpp

source/Lib/CommonLib/Unit.h

source/Lib/CommonLib/UnitTools.cpp

source/Lib/CommonLib/UnitTools.h

source/Lib/DecoderLib/CABACReader.cpp

source/Lib/DecoderLib/DecCu.cpp

source/Lib/EncoderLib/CABACWriter.cpp

source/Lib/EncoderLib/EncCu.cpp

source/Lib/EncoderLib/EncCu.h