add opt-in hide to system tray icon (#99)

src/windows/mainwindow.cpp

@@ -401,4 +401,4 @@ MainWindow::type_signal_action_view_pins MainWindow::signal_action_view_pins() {
 
 MainWindow::type_signal_action_view_threads MainWindow::signal_action_view_threads() {
     return m_signal_action_view_threads;
-}
+}

src/windows/mainwindow.hpp

@@ -83,6 +83,7 @@ private:
     Gtk::MenuItem m_menu_view_go_back;
     Gtk::MenuItem m_menu_view_go_forward;
 #endif
+
     void OnViewSubmenuPopup();
 
 public: