Bug fix for the spin parameter array always being converted to lowercase.
The is in the data_store.mol_res_spin.SpinContainer._back_compat_hook() method. It always calls the
_back_compat_hook_mf_data() method which converts the spin 'params' list all to lowercase. Now the
_back_compat_hook() method first checks that the data pipe is that of a model-free analysis.
