allow reading and restoring the state of the random module

See merge request ift/nifty!435

Extend MatrixProductOperator to be able to operate on subdomains of fields

See merge request ift/nifty!433

Use a generator for MetricGaussianKL.samples

See merge request ift/nifty!432

Use the same logic for returning the samples from the various MPI tasks
as for working with them in each task.

# Conflicts:
#   nifty6/minimization/metric_gaussian_kl.py

Fix KL

See merge request ift/nifty!429

metric_gaussian_kl.py: Fix samples property

See merge request ift/nifty!431

Gordian Edenhofer authored Mar 25, 2020 and Martin Reinecke committed Mar 25, 2020

Fix a bug which was introduced in eded7903 making it impossible to
access the sample property of a KL with mirrored samples as a list can
not be added to a tuple in python.

Linearization logic fixups

See merge request ift/nifty!427

Switch to new numpy random generators

See merge request ift/nifty!428

# Conflicts:
#   nifty6/__init__.py