refactor: rename DiagramGRiwrm into plot.GRiwrm

Fix #12
3 jobs for 12-diagram-of-calibrated-model in 21 minutes and 15 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Checks
passed check_as_cran #174447
docker

00:11:31

passed check_not_cran #174446
docker

00:09:16

 
  Website
passed website #174448
docker

00:09:44