Adds a Engine::Scene to manage the current Scene.
Adds Interface::Window class.

This class is a drawing delegate for any interface component. These will
eventually also receive, like many other Objects, action events, but
they will be unbindable. I will create a bunch of stock widgets
(buttons, labels, text fields). I have added a Label drawing function,
but I don't have the ability to render text.

Therefore, I will have to compile in FreeType for font rendering, but
do something fancy to improve the rendering. Window objects nest, so
I can add caching at certain levels of the tree once the system
determines they do not (or even can not) change. Some of the rendering
can be done and then cached concurrently.

Now, I must figure out how to handle other events with these objects.
And also how to pass along a drawing context and the true position
(relative to the screen or to the most immediate frame buffer). This
will probably be contained within the drawing context.

The drawing context will have to contain references to Fonts, Brushes,
Pens, Textures or so and etc. Not sure yet. Might just make everything
bitmapped... but it might be nice to port over my hardware accelerated
vector code. Probably run curve and anti-aliasing code on the GPU. (I
have much of that code lying around somewhere)