WELCOME BACK, NICKNick Diaz certainly knows how to return to the limelight. His win over BJ Penn on Saturday night was the single most impressive performance of his career by leaps and bounds. Not only did he put his ethereal fighting skills on display in front of millions of fans, proving that he deserves to be regarded as one of the very best in the sport, pound for pound. He also showed tremendous heart and courage by surviving a very rocky first round, one that left him bloodied and swollen…