Enhanced Tiled integration. Can now reload a map that has changed

externaly. Still some rough edges, notably the number of nitification
sto skip when saving in ATCS.

src/com/gpl/rpg/atcontentstudio/model/maps/SpawnArea.java

@@ -64,6 +64,7 @@ public class SpawnArea extends MapObject {
 			}
 		}
 		if (replacedIndex >= 0) {
+			oldOne.removeBacklink(parentMap);
 			spawnGroup.set(replacedIndex, (NPC) newOne);
 			newOne.addBacklink(parentMap);
 		}