UNITY — A business aimed at expanding access to local food and creating new markets for farmers will open its new headquarters this week in a restored two-room schoolhouse on School Street. The Unity Food Hub started operations last year, but was working from a temporary location while renovation of the 19th-century schoolhouse was completed. The concept of a food hub to aggregate, market and distribute food from local farmers isn’t new, said general manager Matt Tremblay in a recent tour of the building. “Farming is alive and well in Maine, and it has a lot of good products,” Tremblay said.