Move NuGet.config up one level where VS can see it

NuGet.config files can be found by VS package restore so long as they're
in a parent directory of the sln.

Copy the file one level higher to align with that. Once the buildtools
are updated, the old copy can be deleted.
Merge pull request #233 from nguerrera/move-up-nuget-config

Move NuGet.config up one level where VS can see it