Merge branch 'add_nfft' into 'NIFTy_5'

Add NFFTOperator

See merge request !304
9 jobs for v5.0.1 in 8 minutes and 42 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Build Docker
passed build_docker_from_cache #768568

00:00:16

 
  Test
passed test_mpi #768570

00:04:22

passed test_serial #768569

00:05:10

80.0%
 
  Demo Runs
passed run_bernoulli #768575

00:00:29

passed run_curve_fitting #768576

00:00:27

passed run_getting_started_1 #768572

00:00:33

passed run_getting_started_2 #768573

00:01:22

passed run_getting_started_3 #768574

00:03:14

passed run_ipynb #768571

00:01:35