handle close request per state

src/yugecin/opsudance/core/state/BaseOpsuState.java

@@ -19,6 +19,11 @@ package yugecin.opsudance.core.state;
 
 public abstract class BaseOpsuState implements OpsuState {
 
+	@Override
+	public boolean onCloseRequest() {
+		return true;
+	}
+
 	@Override
 	public boolean keyPressed(int key, char c) {
 		return false;

src/yugecin/opsudance/core/state/OpsuState.java

@@ -27,6 +27,11 @@ public interface OpsuState {
 	void enter();
 	void leave();
 
+	/**
+	 * @return true if closing is allowed
+	 */
+	boolean onCloseRequest();
+
 	/**
 	 * @return false to stop event bubbling
 	 */

src/yugecin/opsudance/core/state/transitions/TransitionState.java

@@ -71,4 +71,9 @@ public abstract class TransitionState extends BaseOpsuState {
 		listener.onFinish();
 	}
 
+	@Override
+	public boolean onCloseRequest() {
+		return false;
+	}
+
 }