You might think an eight-part miniseries about screen legends Bette Davis and Joan Crawford butting heads and being fabulous would have little to say about modern times. Without soft-pedaling any of the fun and fabulousity of vintage Hollywood, “Feud: Bette and Joan,” which premieres on FX on Sunday at 10 p.m. EST, exposes a not-so-glitzy side of Tinseltown – while framing issues all too prevalent even now.