The secret's been out about Longchamp for a while now.  The fine French bag maker was leading a dignified if sleepy existence when all of a sudden Kate Moss started showing up in the ad campaigns about four years ago. Mini collections by American designer Jeremy Scott among others turned the Longchamp classic "Le Pliage" foldaway into a modern hit desired by all.  Last night, Moss, Longchamp and about 700 friends celebrated the launch of Kate Moss for Longchamp, a new brand designed by Moss for the house, at the Ritz club in Paris. READ THE FULL DESCRIPTION BY REBECCA VOIGHT.