* Create all items in $nav_urls at the beginning so that we don't need to bother...

* Create all items in $nav_urls at the beginning so that we don't need to bother if they are set or not after that
* Don't show 'whatlinkshere', 'recentchangeslinked' and 'trackbacklink' items if OutputPage::isArticleRelated() is false
* Simplify the code to check if we show show user related items since the actual code is just to check if we have an User object
* Moved the showEmailUser() check to the same location as other related user checks
* Made Skin::showEmailUser() accept an User object instead of doing object -> int -> object conversion
* Check if the items are present in BaseTemplate::getToolbox() instead of 'notspecialpage' and removed some empty() or isset() checks since all of these items are now set