The introduction of the Maserati Ghibli next year will mark the first time that the Italian automaker has two four-door models for sale at the same time. This midsize sedan to the venerable Quattroporte is part of a larger effort to lift worldwide Maserati sales from last year’s 6,288 to 50,000 by 2015. While Maserati does not envision itself in the same league as BMW or Jaguar when it comes to volume, this new lofty goal will break it out of the territory occupied by such boutique makes as Ferrari and Aston M…