Loads up the data for editing a poll.

• Must be called with a topic specified in the URL.
• If the user is adding a poll to a topic, must contain the variable 'add' in the url.
• Uses the Post language file.
• Uses the Poll template (main sub template).
• User must have poll_edit_any/poll_add_any permission for the relevant action.
• Otherwise must be poll starter with poll_edit_own permission for editing, or be topic starter with poll_add_any permission for adding.
• Is accessed via ?action=editpoll.