new Callback(thisContext, functionPointer)
 This class is used to describe a
                callback method/function. If the callback is a method:
                
              - thisContext should be a reference to the instance of the object providing the method.
- functionPointer should be a pointer to the method (e.g. "this.getProperty")
- thisContext should be null.
- functionPointer should be a pointer to the function (e.g. "getProperty")
Parameters:
| Name | Type | Description | 
|---|---|---|
| thisContext |  | a reference to the instance of a class providing the callback method or null if the callback is a function | 
| functionPointer |  | a pointer to a method of a class or a function |