macOS: system tray behaviour

Do not open/close Jami on click on the Jami system tray icon.
Click on Jami system tray icon trigger context menu with options
to show Jami and to close Jami.

Change-Id: I2230cc958d23b6aff245a6eca6e7d0776f6a1687

src/mainapplication.cpp

@@ -374,7 +374,7 @@ MainApplication::initSystray()
                 if (reason != QSystemTrayIcon::ActivationReason::Context) {
 #ifdef Q_OS_WINDOWS
                     restoreApp();
-#else
+#elif !defined(Q_OS_MACOS)
                     QWindow* window = focusWindow();
                     if (window)
                         window->close();