Added Segments unit tests.

src/TNL/Containers/Segments/CSR.h

src/TNL/Containers/Segments/CSR.hpp

src/TNL/Containers/Segments/Ellpack.h

src/TNL/Containers/Segments/Ellpack.hpp

src/TNL/Matrices/SparseMatrix.hpp

src/UnitTests/Containers/CMakeLists.txt

src/UnitTests/Containers/Segments/CMakeLists.txt

src/UnitTests/Containers/Segments/SegmentsTest.hpp

src/UnitTests/Containers/Segments/SegmentsTest_CSR.cpp

src/UnitTests/Containers/Segments/SegmentsTest_CSR.cu

src/UnitTests/Containers/Segments/SegmentsTest_CSR.h

src/UnitTests/Containers/Segments/SegmentsTest_Ellpack.cpp

src/UnitTests/Containers/Segments/SegmentsTest_Ellpack.cu

src/UnitTests/Containers/Segments/SegmentsTest_Ellpack.h