Enterprise.active_distributors finds active distributors by product distributions
Rewrite scope with outer join
Enterprise.active_distributors finds active distributors by order cycles
Enterprise.active_distributors doesn't show distributors of deleted products
Enterprise.active_distributors doesn't show distributors of unavailable products
Enterprise.active_distributors doesn't show distributors of out of stock products
Enterprise.active_distributors doesn't show distributors from inactive order cycles