How does Kelly Clarkson celebrate her two Academy of Country Music wins? By singing Britney Spears' pop hit "Til the World Ends," of course! "I thought this might be a fun one that you all might enjoy," Clarkson told the crowd at a recent concert. "I'm going to sing it a little differently ... I love that song." Clarkson covered the pop princess' hit single Tuesday night in Los Angeles, as a part of her nationwide Stronger tour, but she put her own acoustic spin on the infamous dance track. The...