Alan Rickman, the deep-voiced stage and screen actor who began his Hollywood film career as "Die Hard" (1989) villain Hans Gruber, and made his name with a new generation of filmgoers as the black-haired potions master Severus Snape in eight "Harry Potter" films, died in London Thursday after suffering from cancer. He was 69.  Coming just days after the musician David Bowie, also 69, succumbed to cancer, Rickman's death marks a second major blow to the British arts and entertainment world this week. Rickman first distinguished himself as a seductive leading man in London's West End, turning in a breakthrough 1986 performances as Valmont, in "Les Liaisons Dangereuses," and he remained a lifelong devotee of the theatre. Hollywood, perhaps to its discredit, largely failed to see his sex appeal, preferring instead to capitalize on his unmatched ability to convey disdain, even menace.   As Gruber, the Sheriff of Nottingham ("Robin Hood:...