Xfce 4.16 Support
- Add Xfce 4.16 panel layout
- Replace exo-.desktop with xfce4-.desktop launchers
- Fix loading of desktop and whiskermenu files (Closes #11 (closed))
- Refresh all existing layouts with xfce-4.16-compatible settings
- Add whiskermenu configs for Xubuntu 14.04 and 18.04
- Add lower panel transparency for Xubuntu 12.04
- Enable closing app with keyboard interrupt