Plotting

See merge request !70

Martin's monster merge part 5/N: final cleanups, fixes and new testcases

See merge request !68

This reverts commit fc6f126c.

This reverts commit 7c097668.

Master

See merge request !69

# Conflicts:
#   nifty/config/nifty_config.py

# Conflicts:
#	nifty/operators/fft_operator/transformations/gllmtransformation.py
#	nifty/operators/fft_operator/transformations/lmgltransformation.py

Martin's monster merge part 4/N: revamp dependencies, switch to pyHealpix

See merge request !67

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

# Conflicts:
#	nifty/spaces/lm_space/lm_space.py

Martin's monster merge part 3/N: rework tests to avoid npz files

See merge request !66

Martin's monster merge part 2/N: partial de-cythonization

See merge request !65