By Emma Farge and Jennifer Rigby LONDON (Reuters) – World Health Organization members formally agreed on Tuesday to a plan to overhaul its funding model which has been described as “fundamentally rotten” due to its over-reliance on the whims of donors. The plan, which members had already agreed to on a preliminary basis last month, is seen as one of the most important likely outcomes of the U.N. agency’s ongoing annual World Health Assembly in Geneva this week, at which the body is seeking a central role in global health policy. The agreement would mean that obligatory fees rise to up to 50% o…