Move delivery_class out of app_worker (except for sequential_send).
Merge branch 'develop' into develop-frontend

Conflicts:
	go/apps/bulk_message/tests/test_new_views.py
	go/apps/bulk_message/tests/test_views.py
	go/apps/sequential_send/tests/test_views.py
	go/apps/subscription/tests/test_views.py
	go/apps/surveys/tests/test_new_views.py
	go/apps/surveys/tests/test_views.py
Merge branch 'develop-frontend' of github.com:praekelt/vumi-go into develop-frontend