Merge branch 'fix-sandwich-inverse-sampling' into 'NIFTy_4'

Fix Sandwich Operator Inverse sampling

See merge request ift/NIFTy!274
5 jobs for NIFTy_4 in 10 minutes and 38 seconds
Status Name Job ID Coverage
  Build Docker
passed build_docker_from_scratch #638592

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  Test
passed test_python2_with_coverage #638593

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80.0%
passed test_python3 #638594

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  Release
passed pages #638595

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  Deploy
passed pages:deploy

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