Merge branch 'relative_imports' into 'master'

switch all local imports to relative, to avoid silent mistakes

See merge request !2
4 jobs for master in 5 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #257390
test_minimal

00:04:02

passed #257391
test_mpi

00:05:18

passed #257392
test_mpi_fftw

00:02:49

passed #257393
test_mpi_fftw_hdf5

00:04:26