New Windows Desktop DX11 Platform [TEST ME!] 

This pull contains a new Windows desktop platform which uses DirectX 11 and associated systems.  This is an alternative to the Windows desktop OpenGL platform.

- Renamed Windows platform to WindowsGL.
- Added new Windows platform targeting DX11.
- Added ResourceCreatedEventArgs and ResourceDestroyedEventArgs.
- Added conditionals for DIRECTX11_1, WINDOWS_MEDIA_ENGINE, and WINDOWS_MEDIA_SESSION.

This platform doesn't have working audio yet... will get to that tomorrow.

I've tested these changes on all the Windows platforms.  It could use testing on Mac, iOS, Android, and Linux.