Add dirty implementation of stencil dealing with symmetric BC

src/mesh/Stencil.hpp

src/mesh/StencilBuilder.cpp

src/mesh/StencilBuilder.hpp

src/mesh/StencilManager.cpp

src/mesh/StencilManager.hpp

src/scheme/PolynomialReconstruction.cpp

src/scheme/PolynomialReconstructionDescriptor.hpp

src/scheme/test_reconstruction.cpp

tests/test_StencilBuilder.cpp