Get the School Level List. 

This is a listing of all of the public domain School Level items. 

Each School Level item is represented by a TScle. The collection of School Level items is represented by a List of TScle. 

Since this data is public, no authentication is required. The returned Auth is used only for status and messages.

[WebMethod(Description = "Gets a list of all school levels")]
public TAuthScleList GetSchoolLevelList();