I've found vacation nirvana for teenagers and it's a place parents will like just as much as teens do.Welcome to Amsterdam. It's got everything, including teen-safe clubs, terrific outdoor markets that, despite the weak dollar, offer some bona-fide bargains, world-class museums and the chance to explore it all by bicycle.In Amsterdam, everyone seems young, fit and, most important to the teens, hip. And there's the appropriate mix of culture, history and quirkiness in a city where