[Direct3D11] Breaking changes of DeviceContext.Map in case MapFlags.DoNotWait is used. Now DeviceContext.Map with MapFlags.DoNotWait will return an empty DataBox is still in used by the GPU.
[Toolkit.Graphics] Add RenderTarget2D implicit cast to Direct3D11.Resource
[Toolkit.Graphics] Add support for Texture.GetData with DoNotWait new flag.
Merge remote-tracking branch 'upstream/master'