ROME (Reuters) – Diesel brand founder Renzo Rosso is considering expanding into jewelery and launching a new project in Japan to fuel growth at his fashion group despite the global economic turmoil. Known as the "king of high-end casualwear", the rockstar-looking businessman is one of the most dynamic figures in a fashion industry threatened by a slowdown in its core markets. A painful recession in southern Europe and a slowdown in China are forcing European brands to come up with new ideas to lure consumers back into their stores. …