Implement Sim class to allow simulation of multiple Airports

[Gregrs400]

Sim class needs to be added for the software to work as intended. This leads to different parts of the code needing new homes, and leads to changes in mechanics. Passenger generation will continue to be handled by the Airport class, and after completing the implementation of the Sim class, the Airport objects. The program will no longer be run from the Airport class, and the main method will be moved to the Sim class. Other changes:

• Airlines: Flight creation, Plane Flight assignment
• Sim: Plane movement, Passenger movement
• Flight creation: choose 2 airports, find plane to assign, find open gate
• 2 generateFlight methods
  • random origin and destination
  • parameterized origin and destination