Output of metrics is confusing when not using an eval set

When evaluating one file (or multiple files without the -e/--eval option), the metrics option assumes this is a development set (it prints [Min. criterion: EER ] Threshold on Development set <...>).

This can be confusing if we want to score one file on its own which could not be a development set file (e.g. to get the EER metrics of only an eval set).

suggestions:

• Change the line script/figure.py:330 and 342 to something like Threshold on file '%s': %s, and keep the notion of Development set only when self._eval == True.
• Allow changing the set name with a new option.