GLOBAL MARKETS-U.S.-China trade fight leads stocks lower, oil sinks on supply fears

* GRAPHIC-World FX rates in 2018: http://tmsnrt.rs/2egbfVh * Trump OKs $50B in tariffs as China vows retaliation * China trade spat sparks sell-off in U.S. soybean futures * European, emerging market stocks down more than 1 percent each * Oil slumps 3 percent (Updates with close of U.S. markets) By Laila Kearney NEW YORK, June 15 (Reuters) - Wall Street ended lower on Friday and global stocks continued to slide after U.S. President Donald Trump announced new tariffs