By Michel Rose, Layli Foroudi and John Irish DENAIN, France (Reuters) -Emmanuel Macron and Marine Le Pen traded blows at a distance on Monday over who would best protect French voters’ purchasing power, kicking off a tense fight to win the presidential election runoff on April 24. Macron, a pro-European centrist who became president in 2017 after easily beating Le Pen when voters rallied behind him to keep the far-right out of power, is facing a much tougher challenge this time. He is slightly ahead in polls, but Le Pen, who ahead of Sunday’s first round successfully tapped into anger over the…