Converts HTML-entities to UTF-8 characters.

• Requires the admin_forum permission.
• Uses the convert_entities sub template of the Admin template.
• Only works if UTF-8 has been set as database and global character set.
• Divided in steps of 10 seconds.
• Linked from the maintenance screen (if applicable).
• Accessed by ?action=admin;area=maintenance;sa=convertentities.