relax SVN archive

Shifted set_selected_sim() to the base class.

Updated the set_selected_sim() method.

Modified the select_all_sims() function to use the model_loop().

Propagation of the spin_id variable.

An important fix for the model-free minimisation code for the merged count_spins() function.

Another fix for the test_count_spins() unit test.

Fixed the test_count_spins() unit test.

Removed the call to count_selected_spins().

Merged the count_selected_spins() function into count_spins().

Wrote the count_molecules() and count_residues() functions.