LONDON (Reuters) - The Spice Girls reunited for a few hours on Tuesday to launch a new musical based on songs that made them one of the biggest bands of the 1990s, but there was time for plenty of laughs, avowals of mutual love and even the odd catty aside. "Viva Forever!", written by British comedian Jennifer Saunders and produced by "Mamma Mia!" mastermind Judy Craymer, opens at the Piccadilly Theatre in London's West End on December 11. ...