Each year, thousands of Greater Bostonians observe Passover through Seder, the ceremonial meal of prayers, blessings and wine retelling the story of the Jews' exodus from ancient Egypt. It’s a tradition passed down from generation to generation all over the world, but it didn’t reach the White House until 2009. Author Richard Michelson wrote about this unique seder in his new children’s picture book, “Next Year in the White House: Barack Obama’s First Presidential Seder.”