Actively managed ETFs are the new frontier for expansion in the fast-growing ETF industry. So far only 17 are on the market. But at least half a dozen firms are in the early stages of developing new products. Proponents say actively managed ETFs give investors access to a manager's expertise along with the trading benefits unique to ETFs. Noah Hamman, CEO of Bethesda, Md.-based AdvisorShares Investments, is leading the charge to popularize