Add Account::QueenbeeIntegration concern (SaaS-only) that bridges
Fizzy's external_account_id to Queenbee's find_by_queenbee_id lookup,
and adapts the bang lifecycle methods to Fizzy's Cancellable module.
Remove dead billing conditional from cancellation mailer — Fizzy is
free-only, there's no charge to stop.
Donal McBreen
98d06947cb