Fix EEG electrode positions in EDF/BDF import.

When importing EDF/BDF files, an optional .htps file can be supplied to
provide electrode coordinates. This commit fixes the way these are
stored in the .info dictionary, so that functions such as
make_eeg_layout can use them.
I don't understand why this should relabeled. I labeled these according to the conventions listed in the mne-manual (pdf p.272): Digitization point which is a cardinal landmark aka. fiducial point.