Still to do: PhaseMapperElectric does not work
             3D reconstruction does not converge

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.

Many Doctring corrections, all plots now have a "show" parameter to not show a
plot at the end of the method (needed for guis and such).
magdata: quiver_plot: axis switch for x-projection, implemented logarithmic
         arrows and scaling feature.
projector: added to_mag_data() method to directly produce a projected
           magnetization distribution.
gui/create_logo: removed (obsolete and unuseful).
gui/mag_slicer: added!

regularisator: new module to represent different regularisation strategies
costfunction: changed to use the new Regularisator classes, changed arguments!
dataset: fixed bug that always displayed the own phase maps instead of provided
reconstruction: changed to use the new Regularisator classes, changed arguments!
scripts/rueffner_file: tried to avoid Memory Error (no success)
scripts/zi_an: added holographic contour plots with overlayd magnetization
scripts/reconstruction_sparse_cg_test: now uses Regularisator classes and plots
                                       phase differences (original - reconstr.)