Merge branch 'load-save-functionality' into 'main'

src/main/java/bitsplease/mummymayhem/GameViewController.java

...ain/java/bitsplease/mummymayhem/MainWindowController.java

...main/java/bitsplease/mummymayhem/MapEditorController.java

src/main/java/bitsplease/mummymayhem/model/GameModel.java

src/main/java/bitsplease/mummymayhem/model/map/Map.java

...e/mummymayhem/model/persistence/CustomMapPersistence.java

...tsplease/mummymayhem/model/persistence/CustomMapSave.java

...please/mummymayhem/model/persistence/GamePersistence.java

...a/bitsplease/mummymayhem/model/utils/DialogDisplayer.java

...ain/java/bitsplease/mummymayhem/model/utils/Renderer.java

src/main/resources/bitsplease/mummymayhem/game-view.fxml

...main/resources/bitsplease/mummymayhem/mapeditor-view.fxml

src/test/java/bitsplease/mummymayhem/UnitTest.java