FileUtil.class.php, WCF.Message.js, WCF.js and some changes in XML files

# WCF.Message.js
added missing parameter to window.open to open a popup instead of a new
tab.
i don’t know which tool you use to minify this.

# FileUtil.class.php
improved formatFilesize methode
added pow function to getMemoryLimit instead of multiple * 1024

# WCF.js
fixed addThousandsSeparator: https://github.com/WoltLab/WCF/issues/1598