Add error messages and organize code

.gitignore

...in/java/bitsplease/mummymayhem/BuildDialogController.java

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/map/Map.java

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

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