THIS YEAR’S THEME for the National Civic League’s “All-America” city awards was “America at 250 – Strengthening Civic Health and Building Trust.” That apparently gave Chelsea a winning edge, as the immigrant-rich city of 40,000 was one of 10 US cities selected for the award, announced two weeks ago. It was the second year in a row the city was selected for the award. Nearly half of Chelsea’s predominantly Latino population was born outside of th…