[WIP] Fix #1378 - Switch to stub resolver, remove pyunbound #1601

Job	Run time
build-docker (internet.nl, docker/Dockerfile, app)	1m 30s
build-docker (unbound, docker/Dockerfile, unbound)	1m 1s
build-docker (linttest, docker/Dockerfile, linttest)	2m 41s
build-docker (test-runner, docker/test-runner.Dockerfile)	58s
build-docker (webserver, docker/webserver.Dockerfile)	1m 6s
build-docker (grafana, docker/grafana.Dockerfile)	1m 24s
build-docker (util, docker/util.Dockerfile)	56s
lint/check	53s
development-environment-test	2m 11s
batch-integration-test	3m 44s
docs	1s
integration-test	4m 57s
test	2m 30s
	23m 52s

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