Reviewed by Linda C. Brinson DEATH ON THE LUSITANIA. By R.L. Graham. Macmillan. 381 pages. $18.99. On May 1, 1915, the RMS Lusitania, one of the most luxurious ocean liners then sailing the seas, left New York City, bound for Liverpool, England. Six days later, on the afternoon of May 7, as the Lusitania was…