Add CAD interface to load shapes from CAD files.

CMakeLists.txt

DDCAD/CMakeLists.txt

DDCAD/include/DDCAD/ASSIMPReader.h

DDCAD/include/DDCAD/InputReader.h

DDCAD/src/ASSIMPReader.cpp

DDCAD/src/CADDictionary.h

DDCAD/src/CADImport.cpp

DDCAD/src/InputReader.cpp

DDCAD/src/plugins/CADPlugins.cpp

DDCore/CMakeLists.txt

DDCore/include/DD4hep/ComponentProperties.h

DDCore/include/DD4hep/Conditions.h

DDCore/include/DD4hep/ConditionsData.h

DDCore/include/DD4hep/Grammar.h

DDCore/include/DD4hep/Objects.h

DDCore/include/DD4hep/OpaqueData.h

DDCore/include/DD4hep/detail/ComponentProperties_inl.h

DDCore/include/DD4hep/detail/ConditionsInterna.h

DDCore/include/DD4hep/detail/Grammar_parsed.h

DDCore/include/DD4hep/detail/Grammar_unparsed.h