JVET-Q0044: slice index with subpictures

...C-SliceConfigExamples/TwoSubpictures_with_EightSlices.cfg

source/Lib/CommonLib/Slice.cpp

source/Lib/CommonLib/Slice.h

source/Lib/CommonLib/TypeDef.h

source/Lib/DecoderLib/DecLib.cpp

source/Lib/DecoderLib/DecLib.h

source/Lib/DecoderLib/VLCReader.cpp

source/Lib/EncoderLib/EncGOP.cpp

source/Lib/EncoderLib/EncLib.cpp

source/Lib/EncoderLib/VLCWriter.cpp