[Editor’s Note: With the Nationals readying to begin their third season in D.C., change is constant and questions abound. Today, like last year, we take a look at the 2007 roster and all the new contributors. Next week, we’ll discuss this year’s most pressing questions with some of the Nats’ best bloggers.] With the Nats preparing to head north from spring training in Viera for their third season on the Anacostia, it’s time to take…