Unified spaces and field_types into single domain object.

nifty/domain_object.py

nifty/field.py

nifty/field_types/field_array.py

nifty/field_types/field_type.py

nifty/nifty_utilities.py

nifty/operators/composed_operator/composed_operator.py

nifty/operators/diagonal_operator/diagonal_operator.py

nifty/operators/endomorphic_operator/endomorphic_operator.py

nifty/operators/fft_operator/fft_operator.py

...rs/invertible_operator_mixin/invertible_operator_mixin.py

nifty/operators/linear_operator/linear_operator.py

nifty/operators/propagator_operator/propagator_operator.py

nifty/operators/smoothing_operator/smoothing_operator.py

nifty/probing/prober/prober.py

nifty/random.py

nifty/spaces/space/space.py

nifty/sugar.py