LOS ANGELES (Reuters) – Controversial rapper Nicki Minaj and country singer Keith Urban joined the "American Idol" judging panel on Sunday, as the ageing Fox show seeks to boost its star power and recapture sliding audiences in a crowded TV talent show field. In a decision that divided "Idol" fans, Minaj, 29, known for her outlandish outfits and headline-making performances, and Urban were confirmed by Fox hours before auditions in front of judges kicked off in New York for the show's 12th season. …