Accessing GUI controls.

Description: To access a GUI control, you must know its window index and control index. You must use LoadWindow and GetControl to obtain these indices. 
Usually a GUI command works only on one type of controls. A wrong control type will cause a Runtime Error and terminates the GUI script (not the game or the engine).

Example: 
        StartWindow = GemRB.LoadWindow(7)
        Label = GemRB.GetControl(StartWindow, 0x0fff0000)
        GemRB.SetText(StartWindow, Label, GEMRB_VERSION)

In the above example we just load a window whose window ID is 7, and store its window index in StartWindow. We also try to find a control whose control ID is 0xfff0000 and resides on the window pointed by StartWindow.
