If Monte Carlo simulations exist and the diffusion tensor parameters were allowed to vary then the
PDB file of the diffusion tensor representation will contain multiple 'SIM' residues, one for each
simulation. The atoms of these residues represent the axes of the simulated tensors and they will
appear as a distribution.
The code for generating the 'AXS' residues has been shifted from 'self.create_tensor_pdb()' into the
functions 'self.generate_spheroid_axes()' and 'self.generate_ellipsoid_axes()'. The code has been
modified to create the 'SIM' residues as well.
