Everyone wants a spin-off. That’s the talk du jour. It’s not enough to just have a franchise, you need solo films to keep that franchise going and going. It’s the new black: release a movie every other year while the main mothership has its flagship super-movie every two or three years, right? Fox hopes to do the same with the “X-Men: Days Of Future Past”series and Mystique (a mooted spin-off while the super-hero team carries on every other few years). And Marvel obviously already has this plan in place: an “Avengers” movie ever few years and in between them they have their solo character movies, “Captain America: The Winter Soldier,” “Ant-Man,” “Thor: The Dark…