PORTLAND, Maine (AP) — Heather and Doug Donahue left careers in teaching and construction behind to follow a dream of opening a dairy farm and cheese-making business in the rolling fields of Maine. The Donahues, who have run Balfour Farm in Pittsfield for four years, have that dream in common with dozens of small business owners in the suddenly cheese-crazy state. Maine has established itself as the state with the fastest-growing artisanal cheese…