For many years, Savannah and Charleston have been billed as rival sister cities. As the story went, both of them had colonial pedigrees — Charleston was founded in 1670, Savannah in 1733 — and airs of patrician gentility engendered by the mansions of their historic districts, but Savannah was the good-times girl compared with her more straight-laced older sibling. This storyline got a big boost in 1994 from the best-selling novel (and subsequent movie) “Midnight in the Garden of Good and Evil,” with a plot that spun on the eccentric high jinks of Savannah life behind closed doors.