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.
`fit_sphere_to_headshape` should indeed look for 'landmark' points, which are of type CARDINAL. Only if these are not present it should look for points of type EXTRA (to retain backwards compatibility). I've reversed the changes in the EDF reader and fixed `fit_sphere_to_headshape` instead.