SKYLAR GREY  You know her voice from hip-hop hits—now it’s time to get to know her  Not many artists rack up four Grammy nominations before releasing a debut album, but Skylar Grey’s career has hardly followed a traditional path. After writing hits and singing hooks for acts like Eminem, Dr. Dre and Lupe Fiasco, Grey is preparing to release her own debut album, Invinsible. “Being a songwriter is a great life, but I can’t imagine ever...