Add Opera Browser Extension

[milan2sky]

The process should be pretty straightforward since Opera supports Chromium-based extensions.

Steps:

• [ ] Test the extension in the Opera browser to ensure compatibility.
• [ ] Package the extension as a .zip file (same process as with Chrome). @MichiSpebach
• [ ] Submit the extension to the Opera Add-ons store. @MichiSpebach Do you want to do it?

I've already added Opera to the integrations section on the landing page, and it’s marked as "coming soon". Also I will link this issue from the integrations page.

[MichiSpebach]

Plebnames is an open protocol, so feel free to go ahead, maybe I have time this weekend or next week (when it is not done yet)