relax SVN archive

Eliminated a number of the specific API parameters relating to dipole-dipole interactions.

These are now provided by the spin.isotope user function and the dipole_pair user functions. The
eliminated parameters are:
'r' - replaced by dipole_pair.set_dist or dipole_pair.read_dist,
'xh_vect' - replaced by dipole_pair.unit_vectors,
'heteronuc_type' - replaced by spin.isotope,
'proton_type' - replaced by spin.isotope,
'attached_proton' - replaced by dipole_pair.define.

Created the spin.isotope user function.

This is designed to be a permanent replacement for the specific analysis API 'heteronuc_type' and
'proton_type' parameters.

Added the nuclear symbol as a wizard graphic.

Added a set of icons for nuclear or isotope related usage.

Deletion of the structure.vectors user function as it has been superseded by dipole_pair.unit_vectors.

Only the user function definition has deleted - the backend code will remain so that it can be used
internally.

Implemented the dipole_pair.unit_vectors user function backend.

This code originates from the generic_fns.structure.main.vectors() function (the structure.vectors
user function backend). The dipole_pair.unit_vectors user function is designed to replace
structure.vectors.

Fixed the call to dipole_pair.unit_vectors in the dauvergne_protocol.py system test script.

Refinement of the dipole_pair user function definitions.

Created the dipole_pair.unit_vectors user function definition.

Created the backend of the dipole_pair.read_dist user function.