tree: Resolve clang-tidy, clazy, compiler warnings

gui/mainwindow.h

@@ -57,7 +57,7 @@ class MainWindow : public QMainWindow
 	void initSettingsTabs();
 	int currentSelectedScale();
 	void processShortcut(int key);
-	bool eventFilter(QObject *object, QEvent *event);
+	bool eventFilter(QObject *object, QEvent *event) override;
 
   private slots:
 	void lineEditReturnPressed();