refs https://github.com/TryGhost/Team/issues/959
Because we were using the pre-existing products to determine a members
status, instead of the products _after_ we have handled the updates to
subscriptions, members with a paid subscription which was later canceled
were changed to 'comped' rather than 'free'. This adds a final check to
set a member to 'free' if their new set of products is empty.
refs https://github.com/TryGhost/Team/issues/542
Importing members with a created_at date will incorrectly create events
for the member for the date of the import. This updates our event
handling to use either the passed created_at date, or in the case of
subscriptions the start_date of the subscription. We're using start_date
for subscriptions rather than created, as this is more accurate because
start_date works correctly for backdated subscriptions in Stripe.
