SERIES FINALE: Fifteen seasons, and it comes down to this. As part of this two-hour last lap for American Idol, many previous winners and prominent also-rans are scheduled to return to perform live, including Carrie Underwood, Fantasia, Katharine McPhee, and Kelly Clarkson, who got very emotional when visiting, and singing, earlier this season. But then it’s time to crown the final idol – and last night, when finalists Trent Harmon and La’Porsha Renae sang for their votes, it t