New game screen

- Thanks to everyone for finishing the controllers for the UI <3
- I cleaned up the code and added documentation. Please review and make sure it's all good.
- **Please push your use cases on the design branch for all of us to see**
- P.S. do all of the controllers have to implement Initializable? I've always seem `public void initialize(URL url, ResourceBundle rb)` everywhere and they've all been empty.