Add a real quit option in menu

[antitoine]

At the moment, there is no simple way to stop the application completely. The ideal would be to add an "Exit" entry in the menu that stops Quest completely.

[hverlin]

You can now use the standard close button on other platforms than macos:
03a1754

[antitoine]

I was thinking more of an option to quit permanently if asked, and thus leave the current behavior when using the cross (a bit like the Slack application). See if it's complicated to add an icon in the bar status?