Merge branch 'cleanup' into 'NIFTy_5'

demos/getting_started_3.py

nifty5/__init__.py

nifty5/data_objects/distributed_do.py

nifty5/data_objects/numpy_do.py

nifty5/extra.py

nifty5/extra/__init__.py

nifty5/extra/operator_tests.py

nifty5/field.py

nifty5/linearization.py

nifty5/minimization/descent_minimizers.py

nifty5/minimization/energy_adapter.py

nifty5/minimization/iteration_controllers.py

nifty5/minimization/kl_energy.py

nifty5/minimization/line_energy.py

nifty5/minimization/line_search.py

nifty5/minimization/line_search_strong_wolfe.py

nifty5/minimization/nonlinear_cg.py

nifty5/multi_field.py

nifty5/plot.py

nifty5/plotting/__init__.py