In 2011, producer Bryan Singer and director Matthew Vaughn (“Kick-Ass”) reinvigorated the X-Men movie franchise by presenting a story from the early days of the franchise’s heroic characters. This necessitated younger versions of many key players, including Professor Charles Xavier and his archrival Magneto. With “Days of Future Past,” Singer takes over directing duties and performs a careful balancing act, mixing the cast of “First Class” with that of the first three “X-Men” films.