GLOBAL MARKETS-Markets slump on gloomy growth outlook

* World Bank cuts growth forecasts, deflation fears grow* Stocks, commodities, yields fall* Safe-haven Japanese yen gains ground against dollar* Legal opinion on ECB bond-buying helps trim losses(Updates prices, adds JPMorgan, U.S. futures)By Lionel LaurentLONDON, Jan 14 (Reuters) - Financial and commodities markets slumped on Wednesday after the World Bank cut its growth forecasts for 2015 and 20