Update GitHub samples with the Xaml Swapchain samples

[cjrog]

Adding Xaml App samples to mf GitHub to showcase how to use the Xaml SwapChainPanel for media playback.

Adds:

• BasicMFT implementation (passthrough MFT)
• BasicMFTDll - packages the MFT class into a dll
• XAML Sample - Basic app that uses a SourceReader and swapchain panel to complete video playback
• XAML Sample with MFT Class - adds MFT functionality to the pipeline to show how to manually drive a synchronous MFT
• XAML Sample with MFT dll - Additionally shows how to load and instantiate an MFT from a dll.

More information can be found in the readme.md file.