JVET-AC0139: Unified merge function and updated cfg settings

cfg/encoder_lowdelay_P_vtm.cfg

cfg/encoder_lowdelay_vtm.cfg

cfg/encoder_randomaccess_vtm.cfg

cfg/encoder_randomaccess_vtm_gop16.cfg

doc/software-manual.tex

source/App/EncoderApp/EncApp.cpp

source/App/EncoderApp/EncAppCfg.cpp

source/App/EncoderApp/EncAppCfg.h

source/Lib/CommonLib/ContextModelling.cpp

source/Lib/CommonLib/ContextModelling.h

source/Lib/CommonLib/TypeDef.h

source/Lib/CommonLib/UnitTools.cpp

source/Lib/CommonLib/UnitTools.h

source/Lib/EncoderLib/EncCfg.h

source/Lib/EncoderLib/EncCu.cpp

source/Lib/EncoderLib/EncCu.h

source/Lib/EncoderLib/EncModeCtrl.cpp

source/Lib/EncoderLib/InterSearch.cpp