Make AtomicStructureAdapter interface more like vector.

This allows easies wrapping of AtomicStructureAdapter in
boost::python::vector_indexing_suite.  Add few more
proxy methods to vector.  Rename method remove --> erase.
Fix atomBareSymbol crash on empty strings.
Use more standard names for Atom positions and APDs.

Rename data members of the Atom class
cartesianposition --> xyz_cartn
cartesianuij --> uij_cartn
Support client serialization of the Atom class.