fixes https://github.com/TryGhost/Team/issues/2542
fixes https://github.com/TryGhost/Team/issues/2543
fixes https://github.com/TryGhost/Team/issues/2544
- Hides incomplete subscriptions
- Shows Past Due subscriptions
- Fixed UI issues with 3+ subscriptions
- Fixed missing complimentary subscription when one subscription was
incomplete/inactive
- Fixed sending a paid subscription started email for incomplete
subscriptions. This change also required us to actually send the email
when the incomplete subscription eventually becomes active. So the
introduction of a new `SubscriptionActivatedEvent` made sense/was
required (because sending a SubscriptionCreatedEvent again would cause
other issues).
