Scooter Braun’s SB Projects since its founding in 2007, Allison Kaye has helped to shape the careers of superstars like Justin Bieber and Ariana Grande — and has been by Braun’s side through all the ups and downs of the ever-evolving music industry.Now president of SB Projects and a partner in Ithaca Holdings — Braun’s media company that just sold for $1 billion — Kaye is one of the most powerful executives in the business, shepherding both the company’s music and non-music ventures, which now