Rewrite metrics stuff on top of new vumi metrics manager.
publish_oneshot_metrics -> publish_metrics
Django MetricPublisher implements appropriate interface.
Better get_published_metrics() helper.
Remove unused import.
Merge branch 'develop' into feature/issue-915-metrics-api
Pass publisher instead of amqp_client into VumiApi.from_config_async().
Clean up command and event publishers and remove unnecessary configuration.
Add the group action state to the dialogue state type <select>
Add a GroupStateModel
Add a groups relation to the dialogue model
Add boilerplate for dialogue group state views
Change GroupStateModel to not be storable on the contact
Use 'screen' instead of 'question' as the term for 'states' in the UI
Merge branch 'develop' into feature/issue-932-better-VumiApi-publisher-setup

Conflicts:
	go/vumitools/app_worker.py
Add group state to dialogue model fixture (fixing tests that broke because of the change)
Add group model relation to dialogue group state model
Add a reverse relation to the dialogue model to dialogue states
Basics for the client side of the dialogue group state
Only migrate contacts that need migrating.