Support for NuGet packages #3157

There doesn't seem to be a way for node-gyp to generate a packages.config + required goop in the generated vcxproj, so that certain NuGet packages are referenced by the generated project.

Our project references a couple of NuGet packages, which bring in Windows metadata files (.winmd), headers and build-time logic (cppwinrt).

The workaround for now seems to be to check in the generated headers instead of relying on cppwinrt generating the headers at build time, however this is fragile as different cppwinrt versions are not necessarily ABI compatible.