Implementation of the Regularisator class

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.)