Refactored C++ version to bundle all backend stuff into ipaaca-participants

ipaacalib/cpp/CMakeLists.txt

ipaacalib/cpp/include/ipaaca/ipaaca-buffers.h

ipaacalib/cpp/include/ipaaca/ipaaca-converters.h

ipaacalib/cpp/include/ipaaca/ipaaca-forwards.h

ipaacalib/cpp/include/ipaaca/ipaaca-internal.h

ipaacalib/cpp/include/ipaaca/ipaaca-ius.h

ipaacalib/cpp/include/ipaaca/ipaaca-participants.h

ipaacalib/cpp/include/ipaaca/ipaaca-payload.h

ipaacalib/cpp/include/ipaaca/ipaaca.h

ipaacalib/cpp/src/ipaaca-buffers.cc

ipaacalib/cpp/src/ipaaca-converters.cc

ipaacalib/cpp/src/ipaaca-internal.cc

ipaacalib/cpp/src/ipaaca-iuinterface.cc

ipaacalib/cpp/src/ipaaca-ius.cc

ipaacalib/cpp/src/ipaaca-links.cc

ipaacalib/cpp/src/ipaaca-participants.cc

ipaacalib/cpp/src/ipaaca-payload.cc

ipaacalib/cpp/src/util/notifier.cc