tweaks; added some FIXMEs

nifty5/library/amplitude_model.py

nifty5/library/bernoulli_energy.py

nifty5/library/correlated_fields.py

nifty5/library/gaussian_energy.py

nifty5/library/point_sources.py

nifty5/library/poissonian_energy.py

nifty5/multi/block_diagonal_operator.py

nifty5/multi/multi_domain.py

nifty5/operators/multi_adaptor.py

nifty5/sugar.py