Merge branch 'master' of gitlab.mpcdf.mpg.de:ift/NIFTy

demos/wiener_filter_hamiltonian.py

nifty/energies/line_energy.py

nifty/field.py

nifty/minimization/conjugate_gradient.py

nifty/minimization/descent_minimizer.py

nifty/minimization/vl_bfgs.py

nifty/operators/composed_operator/composed_operator.py

nifty/probing/mixin_classes/trace_prober_mixin.py

test/test_operators/test_composed_operator.py

test/test_operators/test_diagonal_operator.py

test/test_operators/test_fft_operator.py

test/test_operators/test_response_operator.py

test/test_operators/test_smoothing_operator.py