`bob.measure.cmc` and `bob.measure.recognition_rate` are not prepared for an open-set identification

Created by: tiagofrepereira2012

Today the functions bob.measure.cmc and bob.measure.recognition_rate does not support a decision threshold as an argument.

This constrain the scope of these functions only for closed-set identification tasks. I suggest to add an optional keyword argument called threshold for that purpose in these functions. This may impact bob.measure.cmc_four_column and bob.measure.cmc_five_column