Editor’s Note: The Sentinel sports staff is putting together a summer series looking at the legacies of the most influential African-American athletes in history. Today: Jack Johnson.Famed documentary filmmaker Ken Burns said of boxing legend Jack Johnson, "For more than 13 years, Jack Johnson was the most famous and the most notorious African-American on Earth."With a description like that, there ought to be quite a legacy behind it.And what a legacy it is.From 1908 to 1915, Johnson was