Warn when screenshot effect isn't available on Wayland, exit if no GUI
Not sure if I'll be able to get this through the translatable string freeze, so the i18n() call is in a separate commit right now.
@teams/vdg I'd like opinions about the message. It's a bit technical because it needs to be in order to explain why Spectacle won't work, but maybe the wording could be better.
Edited by Noah Davis