GateHouse Media and its publicly traded publisher New Media Investment Group is deep in talks to buy USA Today owner Gannett — a merger that would make America’s biggest newspaper chain even bigger, The Post has learned. The two parties had been previously reported to be in talks, but it was unclear until now that the deal was for the smaller Gatehouse to buy Gannett, which is already the biggest newspaper chain in the US by circulation. Fairport, NY-based GateHouse — which owns nearly 700 papers across 39 states, including 156 dailies like the Columbus Dispatch in Ohio — is...