JVET-R0294: Allow decoded picture hash SEI messages to be nested in subpicture context

doc/software-manual.tex

source/App/BitstreamExtractorApp/BitstreamExtractorApp.cpp

source/App/BitstreamExtractorApp/BitstreamExtractorApp.h

source/App/EncoderApp/EncApp.cpp

source/App/EncoderApp/EncAppCfg.cpp

source/App/EncoderApp/EncAppCfg.h

source/Lib/CommonLib/TypeDef.h

source/Lib/DecoderLib/SEIread.cpp

source/Lib/EncoderLib/AnnexBwrite.h

source/Lib/EncoderLib/EncCfg.h

source/Lib/EncoderLib/EncGOP.cpp

source/Lib/EncoderLib/EncGOP.h

source/Lib/EncoderLib/SEIEncoder.cpp

source/Lib/EncoderLib/SEIEncoder.h