[WIP] Fix #1378 - Switch to stub resolver, remove pyunbound #1604

Job	Run time
build-docker (internet.nl, docker/Dockerfile, app)	1m 30s
build-docker (unbound, docker/Dockerfile, unbound)	1m 18s
build-docker (linttest, docker/Dockerfile, linttest)	2m 34s
build-docker (test-runner, docker/test-runner.Dockerfile)	1m 8s
build-docker (webserver, docker/webserver.Dockerfile)	1m 18s
build-docker (grafana, docker/grafana.Dockerfile)	55s
build-docker (util, docker/util.Dockerfile)	1m 2s
lint/check	59s
development-environment-test	2m 11s
docs	1s
test	2m 26s
integration-test	5m 5s
batch-integration-test	2m 58s
	23m 25s

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