Replace "Complete List" with language file entry (Who's Online)

It looks like I accidentally mangled the pull request by referencing master. Stand by while I try to fix that.

On a perusal of the whosonline.php file I noticed that the text for the "Complete List" link was entered directly into the template rather than being read from a language file. I added an entry to the asb_addon language file for it and replaced the directly entered text with a reference to the language entry.