Do not pass inverters around anymore where it is not necessary

demos/Wiener_Filter.ipynb

demos/critical_filtering.py

demos/nonlinear_critical_filter.py

demos/nonlinear_wiener_filter.py

demos/paper_demos/cartesian_wiener_filter.py

demos/paper_demos/wiener_filter.py

demos/poisson_demo.py

demos/sampling.py

demos/tomography.py

demos/wiener_filter_data_space_noiseless.py

demos/wiener_filter_easy.py

demos/wiener_filter_via_curvature.py

demos/wiener_filter_via_hamiltonian.py

nifty5/library/nonlinear_power_energy.py

nifty5/library/nonlinear_wiener_filter_energy.py

nifty5/library/poisson_energy.py

nifty5/library/wiener_filter_curvature.py

nifty5/library/wiener_filter_energy.py

nifty5/minimization/energy_sum.py

nifty5/operators/inversion_enabler.py