[Direct3D11] Add Device.IsSupportedFeatureLevel, remove CheckError on D3D11.CreateDevice in this case to avoid SharpDXException being catched
[Toolkit.Game] Port back support for WinRT SwapChainBackgroundPanel to new GameContext and internals GamePlatform/GameWindow.
[Toolkit.Game] Plug back WP8 DrawingBackgroungSurface support with new GameContext and internal GameWindow