Add a StencilManager mechanism + performances tests and improvements

src/algebra/ShrinkMatrixView.hpp

src/algebra/ShrinkVectorView.hpp

src/language/modules/SchemeModule.cpp

src/main.cpp

src/mesh/CMakeLists.txt

src/mesh/Connectivity.cpp

src/mesh/Connectivity.hpp

src/mesh/StencilBuilder.cpp

src/mesh/StencilBuilder.hpp

src/mesh/StencilManager.cpp

src/mesh/StencilManager.hpp

src/scheme/CMakeLists.txt

src/scheme/PolynomialReconstruction.cpp

src/scheme/PolynomialReconstruction.hpp

src/scheme/test_reconstruction.cpp

src/scheme/test_reconstruction.hpp

src/utils/PugsTraits.hpp

tests/mpi_test_main.cpp

tests/test_StencilBuilder.cpp

tests/test_main.cpp