Small consistency fixes for spaces and FFTOperators.

nifty/domain_object.py

nifty/field.py

nifty/operators/fft_operator/fft_operator.py

...rators/fft_operator/transformations/gllmtransformation.py

...rators/fft_operator/transformations/hplmtransformation.py

.../fft_operator/transformations/lm_transformation_helper.py

...rators/fft_operator/transformations/lmgltransformation.py

...rators/fft_operator/transformations/lmhptransformation.py

...y/operators/fft_operator/transformations/rg_transforms.py

...rators/fft_operator/transformations/rgrgtransformation.py

.../operators/fft_operator/transformations/transformation.py

nifty/spaces/gl_space/gl_space.py

nifty/spaces/hp_space/hp_space.py

nifty/spaces/lm_space/lm_space.py

nifty/spaces/power_space/power_space.py

nifty/spaces/rg_space/rg_space.py

nifty/spaces/space/space.py