Fix/update inline documentations in GlobalFunctions

I mainly fixed PHPDoc comments that are highlighted by PHPStorm
as being wrong or incomplete.

* Fixed some wrong inline documentations, e.g. wrong @return types.
* Used the style suggested by the Doxygen and phpDocumentor
  documentations: @param type [$optional,...]
* Doxygen and phpDocumentor suggest the order: @param type $var
* Avoid unclear "varargs" and "mixed" if possible.
* Lowercased "array" and such, they are no classes.

Change-Id: Iff16e05fed6652cefec29e3d254807f52d84c9ab