Add messages.pot for LaunchPad online translations

[epcim]

I am about to provide Czech translations. This PR just adds po/messages.pot as it is needed for LP translations to discover messages used. Once merged I would switch the main branch on LP to your upstream instead of mine fork.

Question: you are using en_QQ, as probably it is better readable in the terminal for kids. For any translation, I prefer to treat .po files without "spaces" between letters. Can you draft what way we automate the generation of cz_QQ variant? BTW: Not sure if related, but LP offers for English (https://translations.launchpad.net/terminal-quest/+add-custom-language-code) an English code en@quote and en@boldquote.

If you are interested in the LP translations, would be great to add one of our users/emails to the ownership of the LP project I started.

See more here: https://translations.launchpad.net/terminal-quest