A 28-year-old man is being sought in connection with the bomb blast that injured 29 people in Chelsea on Saturday night — and authorities are investigating the possible existence of a local terror cell, sources told The Post. Ahmad Khan Rahami, a US citizen from New Jersey who was born in Afghanistan, could be armed and dangerous, Mayor Bill de Blasio said. “We need to get this guy in right away,” de Blasio said on CNN. “My experience is once the FBI zeroes in on someone, they will get them.”(nypost.com)…[+]