Need more evidence of the increasing importance and influence of anime and manga on the U.S. comic book scene?   How about Wizard World Chicago holding its first ever 'cosplay' event and contest at this year's convention, which will be held at the Rosemont Convention Center, outside Chicago from August 8-10.  The event will be held on Saturday night, August 9 and prizes will include rare DVDs, video games, and t-shirts.  Long a staple of anime conventions both here and in Japan, cosplay events feature fans dressed as their favorite anime and manga characters.   Winners and many other entrants will have their pictures reproduced in the next issue of Anime Insider, the anime magazine published by Wizard Entertainment.