rework imports; tweak domain comparisons

nifty5/compat.py

nifty5/data_objects/distributed_do.py

nifty5/data_objects/random.py

nifty5/domain_tuple.py

nifty5/domains/log_rg_space.py

nifty5/domains/rg_space.py

nifty5/domains/unstructured_domain.py

nifty5/energies/kl.py

nifty5/extra/energy_and_model_tests.py

nifty5/field.py

nifty5/logger.py

nifty5/minimization/energy_sum.py

nifty5/minimization/iteration_controller.py

nifty5/minimization/l_bfgs.py

nifty5/minimization/line_search_strong_wolfe.py

nifty5/minimization/vl_bfgs.py

nifty5/operators/chain_operator.py

nifty5/operators/diagonal_operator.py

nifty5/operators/fft_operator.py

nifty5/operators/sht_operator.py