[EPIC] Add a minimal Steering unit test suite

Parent: [EPIC] Basic test coverage for all services (aura#175)

It should at least cover

• the ViewSets in program/views.py:

  • APIHostViewSet
  • APIImageViewSet
  • APINoteViewSet
  • APIScheduleViewSet
  • APIShowViewSet
  • APIUserViewSet

• the conflict resolution code in program/services.py:

  • generate_conflicts
  • generate_timeslots
  • instantiate_upcoming_schedule,
  • make_conflicts
  • resolve_conflicts