Put vertex positions and normals in Vertex struct

surfseg/include/manifold_mesh.h

surfseg/matlab/mex_ksurfcut.cpp

surfseg/matlab/mex_subdiv_icosahedron.cpp

surfseg/matlab/mex_surfcut.cpp

surfseg/matlab/mex_surfcut_planesep.cpp

surfseg/matlab/mex_surfcut_planesep_dual.cpp

surfseg/matlab/mex_surfcut_planesep_qpbo.cpp

surfseg/src/manifold_mesh.cpp

surfseg/src/subdivided_icosahedron.cpp

surfseg/src/surface_segment.cpp