Who knew? Yesterday apparently would have been the 50th wedding anniversary of John F. and Jacqueline Kennedy, and NBC’s “Today” brought on Kennedy social secretary Letitia Baldridge for yet another nostalgic look at old home movies of Jack and Jackie. “It’s so fun to look at that,” cooed Katie Couric. “Why was the country so captivated? I mean this was a huge deal. This was as big as Ben and J-Lo!” Baldridge corrected: “Oh please! Do not compare them.” Couric: “Sorry.” They’re America’s royal family, remember?