Merge branch 'NIFTy_4' into yango_minimizer

demos/critical_filtering.py

demos/krylov_sampling.py

demos/nonlinear_critical_filter.py

demos/nonlinear_wiener_filter.py

demos/poisson_demo.py

demos/wiener_filter_data_space_noiseless.py

demos/wiener_filter_easy.py

demos/wiener_filter_via_hamiltonian.py

nifty4/__init__.py

nifty4/data_objects/distributed_do.py

nifty4/domain_tuple.py

nifty4/domains/domain.py

nifty4/domains/lm_space.py

nifty4/domains/rg_space.py

nifty4/extra/energy_tests.py

nifty4/extra/operator_tests.py

nifty4/field.py

nifty4/library/krylov_sampling.py

nifty4/library/noise_energy.py

nifty4/library/nonlinear_power_energy.py