Merge branch 'simple' into 'main'

src/main/java/view/Grid.java

src/main/java/view/ViewElement.java

src/main/resources/view/DarkTheme.css

src/main/resources/view/view.fxml

src/test/java/model/FirefighterBoardTest.java

src/test/java/view/FirefighterGridTest.java