Use `__new__` to generate Gtk classes.

[cjwelborn]

This will turn self.winMain accesses into self, and allow children to be accessed as 'self.childWin' instead of self.childWin.childWin. The builder needs to be involved in __new__, so it may be a little tricky to instantiate the main window in __new__, and then instantiate all children in __init__ (especially with the current code generation, and regular vs. dynamic init).

The idea came from this article.

More information is needed.