Fixed some memory leaks in GraphicsDevice

Hi,
some objects created by GraphicsDevice were not being disposed correctly. Here are the details:

- GraphicsAdapter -> added call to GraphicsAdapter.Dispose() in GraphicsDevice.Dispose()
- GraphicsOutput -> wrapped in ToDispose(output..)
- object output1 in GraphicsOutput's initialization code was not being disposed in DirectX11.1

I tested it with my current project and I was finally able to report no surviving leaked objects :)