[Fix] Les entités se superposent correctement

src/main/java/app/SimulatorApplication.java

src/main/java/model/Board.java

src/main/java/model/EmptyEntity.java

src/main/java/model/EmptySquare.java

src/main/java/model/EntityScenario.java

src/main/java/model/FireFighterScenario.java

src/main/java/model/Square.java