Mod tools enhanced: conditionally create the header tab menu

Previously, the threshold button was added along with a new tab menu to all pages to account for the pages (ex. mod queue) where one doesn't exist. This behavior causes overlapping with the some customized CSS and can other elements:

![](http://i.imgur.com/n99a6PG.png "Bad-looking overlapping :(")

This change adds a condition to the creation of a new tab menu. It is created in pages on which it doesn't exist and otherwise added to the existing tab menu.