chore(gitlab-ci): use templates and tox similar to other projects

5 jobs for !37 with topic/default/switch-to-gitlab-ci-templates in 50 minutes and 37 seconds (queued for 19 seconds)
latest detached
Status Name Job ID Coverage
  Lint
passed check-manifest #361761

00:01:57

passed flake8 #361760

00:00:31

passed yamllint #361762

00:02:15

 
  Tests
passed py3 #361909

00:48:17

failed py3 #361763

01:57:40