Created MainController class.
MainController is in charge of changing the scene of the game. MainController has a method which changes a scene given the name of the fxml file as a String.
SpaceTrader.java has references to game's Universe and Player. 
Every controller has a method setMainControl which gives the controller a reference to the MainController.
Made spacetrader.system package
Moved all controllers and SpaceTrader.java to system package.
Merge pull request #5 from nkarusala/Integrate_Controllers

Integrate controllers