chore: add boilerplate for a settings dialog

src/MainWindow.h

@@ -10,9 +10,11 @@
 QT_BEGIN_NAMESPACE
 class QSystemTrayIcon;
 class AuthManager;
-class AuthDialog;
 QT_END_NAMESPACE
 
+class AuthDialog;
+class SettingsDialog;
+
 namespace Ui {
 class MainWindow;
 }
@@ -26,7 +28,12 @@ public:
 
     ~MainWindow();
 
-private:
+  private slots:
+    void on_exitButton_clicked();
+
+    void on_settingsButton_clicked();
+
+  private:
     void setupTrayIcon();
 
     QSystemTrayIcon *m_trayIcon;
@@ -34,6 +41,8 @@ private:
 
     AuthManager *m_authManager;
     AuthDialog *m_authDialog;
+
+    SettingsDialog *m_settingsDialog;
 };
 
 #endif //LLINK_MAINWINDOW_H