LONDON (Reuters) - Imperial Brands on Tuesday issued a "cautious" forecast for the year and named a new chairman as the tobacco producer grapples with challenges in e-cigarette products and vaping.The British company said it plans to launch new e-cigarette products and refresh its main e-cigarette brand blu this year with its performance in e-cigarettes and tobacco heating products expected to be more heavily weighted in the second half. The maker of Winston and Gauloises cigarettes reported..