Contemporary music remains a tough sell in most concert halls, so when flutist Claire Chase decided to found her own ensemble specializing in the stuff, she knew she’d better be ready to take her performances outside traditional “classical” spaces. Three years later, Chase’s Chicago-based International Contemporary Ensemble (ICE) is a bona fide cult hit, performing everywhere from chamber music venues to seedy dive bars, and thriving on a combination of youthful energy (nearly all the Icicles, as members of the group are known, are under 30) and serious artistry.