Fill the cup to inhibit auto suspend and screensaver.
This extension supports gnome-shell 3.4 to 3.22.
Use the gnome-shell-before-3.10 branch for gnome shell 3.4, 3.6 and 3.8.
Empty cup = normal auto suspend and screensaver. Filled cup = auto suspend and screensaver off.
https://extensions.gnome.org/extension/517/caffeine/
git clone git://github.com/eonpatapon/gnome-shell-extension-caffeine.git
cd gnome-shell-extension-caffeine
./update-locale.sh
glib-compile-schemas --strict --targetdir=caffeine@patapon.info/schemas/ caffeine@patapon.info/schemas
cp -r caffeine@patapon.info ~/.local/share/gnome-shell/extensions
Restart the shell and then enable the extension.