relax SVN archive

Converted the Molmol 'command_history' structure into a module variable.

Huge redesign of the load_PDB_sequence() function (and converted it to the new relax design).

This new function should give much more flexibility and abstraction in the mapping from the
molecular structure to the relax mol-res-spin data structure.

Finished converting the read_pdb() function to the new relax design.

Converted the load_structures() function to the new relax design.

Replaced all 'relax_data_store.pdb[run]' with 'cdp.structure'.

Removed the adding of the 'run' to the 3D structure data structure.

Deleted the SpecificData container as nothing now uses it.

Changed the 3D structure data structure from a SpecificData class to the Element class.

Removed an unused import of SpecificData.

Updated all the tests of the read_pdb() function to the new relax design.