Bojan Bokic/Getty ImagesNantucket is sleepy in the winter. Billionaires like Google CEO Eric Schmidt and banking titan Charles Schwab have not decamped to their multimillion-dollar vacation homes. Weekenders aren’t wandering the picturesque lanes. Hollywood A-listers are not in town for the annual film festival.But behind the scenes, things are anything but boring. A protracted fight over a housing development with units for low-income residents has entered a bitter new stage, with a slew of cou