Alter en.lernu.net to use HTML5 sound instead of Flash

Adds a button above user nicknames on the search page, clicking it hides that user from search results permanently. Hidden users are remembered between browsing sessions. The hidden users will still appear on other pages, e.g. if they wink at you.

Automatically dismiss the ad that shows when you're not signed in.

Disable Youtube's autoplay setting by checking if it's enabled every 10 seconds and clicking the button if so.