QuickBooks ↔ Median parity per account, to the cent (#2642)

Without asOf, returns the latest stored check (null when none has run). With asOf, reads QuickBooks' TrialBalance as of that date and ProfitAndLoss from the posting cutoff through it, compares each mapped account with Median's GL at a 0-cent tolerance, stores the result and returns it. Before the cutoff the status is not_applicable and QuickBooks is not called. Read-only toward QuickBooks and the GL; a daily check also runs after each completed QuickBooks read. The result is information and never blocks posting or approval.