The city’s first known Trayvon Martin mural is going up on a wall of an East New York laundromat - adding to a brewing campaign to make sure history doesn’t snub the slain teen’s image. Teenage boys will start painting the 100-foot picture July 16 on New Lots Laundromat’s wall underneath the elevated tracks of the IRT No. 3 train. The East New York mural will join a growing list of similar street art popping up in black neighborhoods across the country. “We want him to become a martyr, and it’s sad that we even have to say that,” said...