Mark St. Germain’s play “Relativity” starring Mike Nussbaum as Albert Einstein has been extended at Northlight Theatre in Skokie through June 25. Don’t miss it.Under the direction of BJ Jones, this 70-minute intermission-free drama about the iconic scientific genius is what I would call a what-if piece of creativity.As in what if the Axis powers won World War II as imagined in Philip K. Dick’s novel and TV series “The Man in the High Castle” or Philip Roth’s “The Plot …