Mayor John DeStefano’s New Haven Democratic Town Chairwoman, Susie Voigt (pictured), was easily reelected at a convention at Sports Haven Monday night. But it was a disappointing night for DeStefano’s gubernatorial campaign. His allies had to fight to elect a slate of loyal hometown delegates to the state nominating convention. And the momentum for the state party’s endorsement continued slipping away as yet another big-city mayor lined up behind DeStefano’s opponent.The New Haven Democratic Party convention, usually a humdrum Dean Martin Roast kind of affair, turned into a lively, confusing and crowded evening suffused with gubernatorial politics and festering sores from intraparty squabbles.