By Robert Doyle He is one of the most iconic figures of the American Civil War and, as the commander of the Union Army’s Irish Brigade, Thomas Francis Meagher (right, from from Arthur Griffith's "Meagher of the Sword," Dublin, 1916) is probably the most famous of the Irish-born soldiers who fought during that five-year conflict. And he spent his childhood in County Kildare. Born in County Waterfo…