For many Americans - and undoubtedly for many New Yorkers - memories of September 11, 2001, still sting. Even now, it seems as though there's no amount of distance that can completely salve the wounds that were opened that day. With their new musical at the Gerald Schoenfeld, Come From Away, Irene Sankoff and David Hein try to do so from a remove of about 1,700 miles (give or take), and, perhaps not surprisingly, only intermittently succeed. . . .