refs https://github.com/TryGhost/Team/issues/765
This supercedes the `complimentary_plan` flag, as it is more precise
because it determines _which_ product(s) a member has access to. Because
of this, if the `products` column is present the `complimentary_plan`
column is not used.
refs https://github.com/TryGhost/Team/issues/765
As part of the multiple products feature, we're not longer using Stripe
subscriptions to denote Complimentary access, instead we're linking
members directly to products. Here we update the importer to follow
suit, so long as the flag is enabled.