WEB EXCLUSIVE: The April 23 premiere of Doctor Who is less than a month away, and the anticipation is increasing. Well, that anticipation is just about to get a whole lot more intense. Showrunner Steven Moffat and his team have created a short prequel to the new season exclusively for the web fans, and it’s a marvelously creepy scene that beautifully sets up the Doctor’s next big adventure. (No, the above is not a screencap from The West Wing.) You are advised to watch very carefully…