Intermediat commit on the way to implement norms and more regularizations.

minor changes to plotting methods (PhaseMap now plottable without colorbar).
phase_map: gain can now be set to 'auto' (5 fringes, determined by max. phase).
renamed 'density' to 'gain' (makes more sense).
regularisator: started to include norms and more kinds of regularisations.
mag_slicer: GUI which can go through loaded magnetizations along the major axes.
paper 1: minor changes to the scripts for the results.