By Jonathan Landay WASHINGTON (Reuters) – The United Nations aims to kickstart this month a system to swap millions of aid dollars for Afghan currency in a plan to stem humanitarian and economic crises and bypass blacklisted Taliban leaders, according to an internal U.N. note seen by Reuters. Since the Taliban takeover in August, foreign financial assistance has stopped and international banks are wary of testing U.N. and U.S. sanctions on the hardline Islamist group, leaving the United Nations and aid groups struggling to obtain cash even as they continue to receive humanitarian donations. Th…