Greenwire: In the midst of a worldwide economic crisis, city officials and Wall Street executives are talking about turning the battered U.S. financial center into a global hub of green finance and environmental commodities trading. The spark: draft energy and climate legislation unveiled by two senior House Democrats in Washington this week. The cap-and-trade proposal from Reps. Henry Waxman of California and Ed Markey of Massachusetts has been the talk of the Wall Street Green Trading …