import sensitivities from a directory

        Note
        ----

        * check that signs are correct in case CRMod switches potential
          electrodes

def _read_sensitivities(self, sens_dir):
        """import sensitivities from a directory

        Note
        ----

        * check that signs are correct in case CRMod switches potential
          electrodes

        """
        if self.assignments['sensitivities'] is not None:
            print('Sensitivities already imported. Will not overwrite!')
            return
        else:
            self.assignments['sensitivities'] = {}

        sens_files = sorted(glob(sens_dir + os.sep + 'sens*.dat'))
        for nr, filename in enumerate(sens_files):
            with open(filename, 'r') as fid:
                metadata = np.fromstring(
                    fid.readline().strip(), sep=' ', count=2
                )
                meta_re = metadata[0]
                meta_im = metadata[1]

                sens_data = np.loadtxt(fid)

                cids = self.parman.add_data(
                    sens_data[:, 2:4],
                    [meta_re, meta_im],
                )
                # store cids for later retrieval
                self.assignments['sensitivities'][nr] = cids