A crew of gangbangers — that included a 16-year-old boy — was busted Friday after carrying out a string of gunpoint robberies that netted them $100,000 in stolen jewelry. The alleged Trinitarios members yanked chains and watches off seven victims in a two-week span, including an elderly man who was so shaken he moved out of the Bronx for good, according to Bronx District Attorney Darcel D. Clark.