Added Model Class Vehicle and Car
Ref. //  http://www.raywenderlich.com/45940/intro-object-oriented-design-part-1
Added VehicleListTableViewController and VehicleDetailViewController
Added MotorCycle and Truck Models
Category added - UIAlertView+Convenience
Refer - http://www.raywenderlich.com/45942/intro-object-oriented-design-part-2
Added Factory Methods and Protocol Delegates
Refer - http://www.raywenderlich.com/45942/intro-object-oriented-design-part-2
Added VehicleList Singleton Class and modified VehicleListViewController to fetch the data from singleton class
Refer - http://www.raywenderlich.com/45942/intro-object-oriented-design-part-2