Removed NIFTy 2 files that have not been ported so far.

Modified power_analyze in Field for complex power spectra.

- Add get_default_codomain function in utilities
- Move all transforms to a subfolder inside the fft_operator
- Correct weight method calls in transform method of each transformation

Adapted imports and setup.py to changes.

WIP: Cleaning up the structure of Space classes. Tidied up the chain PowerIndices -> PowerIndexFactory -> Space -> PowerSpace; including paradict.

- get_slice_list returns the entire shape when axes is None
- GFFT.transform() is now a single for-loop
- Input array is simply cast to codomain's dtype
- Other formating changes were included/reverted