Removed Containers::List because it has no benefits over std::list

Documentation/Examples/StringExample.cpp

Documentation/Tutorials/Vectors/Reduction.cpp

src/Examples/CMakeLists.txt

src/Examples/ListExample.cpp

src/TNL/Containers/List.h

src/TNL/Containers/List_impl.h

src/TNL/Images/DicomSeries.h

src/TNL/Images/DicomSeries_impl.h

src/Tools/tnl-dicom-reader.cpp

src/UnitTests/Containers/CMakeLists.txt

src/UnitTests/Containers/ListTest.cpp