Replace Ref{Face,Node}List by a generic RefItemList

src/mesh/Connectivity.hpp

src/mesh/ConnectivityDispatcher.cpp

src/mesh/GmshReader.cpp

src/mesh/MeshNodeBoundary.hpp

src/mesh/RefFaceList.hpp

src/mesh/RefItemList.hpp

src/mesh/RefNodeList.hpp

src/scheme/BoundaryCondition.hpp