Last week, this series brought back Season 1 winner Kelly Clarkson, as both mentor and performer – one of the many ways Idol is trying to invigorate itself, and lure back viewers, in its autumn years. Tonight, it makes room for another former Idol singer turned star: Jennifer Hudson, who didn’t win the year she competed, but afterward, ended up winning an Oscar. And tonight, she sings a duet with Iggy Azalea, one of today’s hottest female singers – but someone who, I susp