added generation number on the GUI

src/main/java/firefighter/controller/Controller.java

src/main/java/firefighter/model/Board.java

src/main/java/firefighter/model/FirefighterBoard.java

src/main/java/firefighter/util/Position.java

src/main/java/firefighter/view/FirefighterGrid.java

src/main/java/firefighter/view/Grid.java

src/main/resources/firefighter/view/view.fxml