Teach the VS 2015 generator to support WindowsStore 10.0 applications.
Add target properties to customize them:
* VS_WINDOWS_TARGET_PLATFORM_MIN_VERSION: Specifies the minimum version
of the OS that the project can target.
* VS_DESKTOP_EXTENSIONS_VERSION, VS_MOBILE_EXTENSIONS_VERSIONS,
VS_IOT_EXTENSIONS_VERSION: Add a reference to the version of the SDK
specified to the target allowing to target the extended functionality in
a universal project.
* VS_IOT_STARTUP_TASK: Specifies that the target should be
built as an IOT continuous background task.
Create properties VS_SHADER_ENTRYPOINT and VS_SHADER_MODEL. Without
these many .hlsl source files may not be possible to use. Extend the
VSWinStorePhone test project to cover them.
Gilles Khouzam
Robert Goulet
Cedric Perthuis