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.
Merge branch 'develop' into feature/issue-932-better-VumiApi-publisher-setup

Conflicts:
	go/vumitools/app_worker.py
Merge branch 'develop' into feature/issue-932-better-VumiApi-publisher-setup
Merge branch 'develop' into feature/issue-915-metrics-api

Conflicts:
	go/vumitools/tests/test_app_worker.py
Merge branch 'feature/issue-932-better-VumiApi-publisher-setup' into feature/issue-915-metrics-api

Conflicts:
	go/vumitools/app_worker.py
Merge branch 'feature/issue-932-better-VumiApi-publisher-setup' into develop
Merge branch 'develop' into feature/issue-915-metrics-api
Update to Django 1.5.8.
Move metric manager setup to VumiApi.
Switch MetricsMiddleware over to new-style metric manager.
Transient VumiApi for MetricsMiddleware.
Use default aggregators from Metric instead of specifying AGG.
Cleaner metric target construction.