LESBOS, Greece, Jan 16 (Reuters) - Over two dozen aid workers involved in refugee rescues in Greece were acquitted of migrant smuggling charges in a multi-year case that rights groups said was a baseless attempt to ban aid for refugees heading to Europe.European Union countries, including Greece - where more than one million people came ashore during Europe's refugee crisis in 2015-16 - are tightening rules on migration as right-wing parties gain ground across the bloc.