Consistently use LaTeX labels in figures instead of relying on psfrag

Thanks for that.

I think there is a bug (already present before your merge request): the various \includegraphics statements (4 occurrences) point to wrong filenames (slightly different from those that are generated by MATLAB and that contain the graph itself).

Could you possibly also fix this? If you want this fix to be on 4.6, please put it in a separate commit, before the one that removes the psfrag stuff.