Changing segments to be compatible with std::plus and simillar functionals.

Documentation/Examples/Matrices/CMakeLists.txt

...Examples/Matrices/DenseMatrixExample_allRowsReduction.cpp

...on/Examples/Matrices/DenseMatrixExample_rowsReduction.cpp

src/TNL/Containers/Segments/BiEllpack.h

src/TNL/Containers/Segments/BiEllpack.hpp

src/TNL/Containers/Segments/BiEllpackView.h

src/TNL/Containers/Segments/BiEllpackView.hpp

src/TNL/Containers/Segments/CSR.h

src/TNL/Containers/Segments/CSR.hpp

src/TNL/Containers/Segments/CSRView.h

src/TNL/Containers/Segments/CSRView.hpp

src/TNL/Containers/Segments/ChunkedEllpack.h

src/TNL/Containers/Segments/ChunkedEllpack.hpp

src/TNL/Containers/Segments/ChunkedEllpackView.h

src/TNL/Containers/Segments/ChunkedEllpackView.hpp

src/TNL/Containers/Segments/Ellpack.h

src/TNL/Containers/Segments/Ellpack.hpp

src/TNL/Containers/Segments/EllpackView.h

src/TNL/Containers/Segments/EllpackView.hpp

src/TNL/Containers/Segments/SlicedEllpack.h