“Glee”? Only in the wake of 13,000-plus stock-market averages would such a title be imaginable. Optimism, confidence, and fun are the watchwords here, and the curators, Amy Cappellazzo (of the Palm Beach Institute of Contemporary Art, where the exhibition will travel next) and the Aldrich’s Jessica Hough, are pretty open about the fact that these twenty artists “skirt weighty subject matter or politicized content.” The show is premised on the idea that painting exists with more conviction now that it has been forced to shed some of its worn conventions and historical baggage in order to survive