big simplifications; power_synthesize() -> draw_sample()

demos/Wiener_Filter.ipynb

demos/critical_filtering.py

demos/nonlinear_critical_filter.py

demos/paper_demos/cartesian_wiener_filter.py

demos/paper_demos/wiener_filter.py

demos/wiener_filter_easy.py

demos/wiener_filter_via_curvature.py

demos/wiener_filter_via_hamiltonian.py

nifty4/__init__.py

nifty4/library/wiener_filter_curvature.py

nifty4/operators/chain_operator.py

nifty4/operators/diagonal_operator.py

nifty4/operators/scaling_operator.py

nifty4/sugar.py

nifty4/utilities.py

test/test_field.py