add XMLLoader module to load widget tree from xml file

[brumazzi]

This "XMLLoader" module reads an XML file and generates the widget structure with the following components:

• Button
• Canvas
• CheckButton
• ComboBox
• Entry
• Fixed
• Frame
• Image
• Label
• Notebook
• ProgressBar
• RadioButton
• Scale
• Scrollbar
• ScrolledWindow
• Separator
• Spinner
• SpinButton
• Table
• ToggleButton
• Window

[TankOs]

Thanks for the MR. Looking at the XML file, it seems to be a very cool feature. I'm unsure whether I'd like to have an XML parser in the core library, though. It adds a dependency and complexity for something only a fraction of SFGUI's users need and will use.

I'll give this a spin to get a feel for it. :)

Btw.: The CI builds fail.