PBS’s first original American drama in more than a decade, Mercy Street follows doctors, nurses, contraband laborers and Southern loyalists in Union-occupied Alexandria, VA in the early years of the Civil War, but could not be more current, co-creator David Zabel told journalists at TCA this afternoon. “This show not a political show – we’re trying to capture a cross-section of characters, as the war is just getting going,” Zabel said in response to a question about…