Resolve "Fix the losscalculator to accept more mappings than needed"

Closes #46 (closed) Sometimes im_types_dict.get(self.intensity_measure_map[im_ff], None) is equal to none, then we receive an error. But we do not care when it is none (which mean there are more mappings given than needed). In this case, in order to ignore None we put it in a for loop and only proceed for the ones that do not None.

\approve @tara @shinde