Add a better confirmation before abandoning an extension

Current behaviour

Clicking on "Abandon" results in a JS confirmation. Some users reported that this JS was not executed and the accidental click lead to an unwanted abandoned extension.

Possible behaviour

When clicking on "Abandon", there will be a new page or a modal where the extension owner needs to confirm this action. For confirming, the owner needs to type in the extension key to delete, like on GitHub and GitLab.