Refactored **transformation.py classes and FFTOperator. Especially fixed RGRGTransformation.check_codomain.

Fixed a few small bugs.

- Refactor RGRGTransformation
- Add is_local to dictionary key hash

Started to consolidate the code base of LM <-> GL/HP transformations.

- 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.