LOS ANGELES (Reuters) - Grammy-winning R&B singer Mary J. Blige has always sung from her heart, telling of personal struggles on albums such as "No More Drama" and "Stronger with Each Tear." She also has dabbled in acting with guest roles on TV's "Ghost Whisperer" and in the Tyler Perry film "I Can Do Bad All By Myself." On Friday, her acting and singing skills will both be on display in her most high-profile film role yet - Justice, owner of the Venus Gentlemen's Club in the rock musical "Rock of Ages. ...