LONDON (Reuters) - Stocks gained amid trade war headlines on Thursday, while sterling rose to its highest in more than two years against the euro on hopes next week's UK election will lead to a smooth Brexit.Belief a trade deal would be struck stemmed from a Bloomberg report on Wednesday that China and the U.S. were close to phase one of a deal and from U.S. President Donald Trump's remarks that talks were going "very well". Trump has said earlier a deal might have to wait until after U.S...