METALS-London copper bounces off three-week low, but trade worries drag

(Adds nickel and China output data, updates prices) By Manolo Serapio Jr MANILA, June 20 (Reuters) - London copper rebounded from a three-week low on Wednesday after losing nearly 2 percent in the previous session, although a deepening trade row between China and the United States capped any recovery in risk appetite. Nickel, up more than 1 percent, was the top gainer while other metals including aluminium and zinc also edged up, but most were not far above multi-week lows reached o