relax SVN archive

Updated the internal PDB structural object to use the self.structural_data object.

The atomic_data structure has been replaced by self.structural_data, and is no longer passed into
each method. The description of this object has also shifted from the methods into the class
docstring.

Corrected some comments.

Corrected calls to the heteronucleus in the opendx system test script code.

Corrected calls to the heteronucleus in the model-free system test code.

Updated the __all__ list.

Removed many unused imports.

Created the internal relax PDB object class.

Spun out all of the functions accessing 'atomic_data'.

These will be converted to methods of a new type of internal PDB object.

Corrected errors causing failures of the unit test for consistency testing variables set up.

The variable 'heteronuc_type' was used instead of 'heteronucleus'.

Partially fixed more code so the consistency tests system test can go further before failure...

Set missing parameter values in system test code.