Auction house tax & listing fees

Returns the sale tax and the price-tiered listing fee schedule so clients can compute exact profits. Sale tax = price * sale_tax_percent/100 (deducted from payout). Listing fee = price * tier.percent/100, where tier is the first listing_fee_tiers entry with price <= max_price. SubPlus subscribers pay sub_plus_multiplier (0.5 = -50%) on both.