add Builtin/yamlgui, with demo

[erladev]

Adding the yamlgui system, for creating LUI objects from an structured yaml file. Current features:

• most (probably all) LUI Classes supported
• Keyword Arguments
• nested structure, template instancing from python code
• python code inside the yaml file
• event binding
• removing / changing UI using a single function

[rdb]

A few suggestions...

• Doesn't seem to be Python 3 compatible due to use of various deprecated syntax (such as implicit relative import, "exec in", etc.)
• Inconsistent use of tabs/spaces, I would suggest sticking to 4 spaces for indentation as is the de facto standard.
• Why define both getitem and getattr to the same thing? It seems redundant.
• Naming convention seems inconsistent, class names should use CamelCase and methods should use snake_case.
• LUIWidgeds should probably be spelled LUIWidgets
• Spacing seems inconsistent, I would suggest one blank line between methods, and never more than two blank lines
• Calling gc.collect() from a destructor seems like an altogether bad idea to me. Is it necessary to call it at all?