Add a system tray context menu

It is common to have one menu for each click (left/right or command on macOS).
We could use 2 behaviors to have at least one reactive menu:

• left click: shows up the current menu as we know but instead of having a second menu (the advanced one), we add a button to suspend/start the current engine.
• right click: shows up the avanced menu without the suspend/restart choice. This one will be light fast to show because we do not need to check engine state nor network checking. Also, we do not have to rebuild it every click.