Also clean up a bunch of issues with the generatenupkg script:
* Output from nuget pack was getting lost
* Non-existent file was imported
* Literal '-ForegroundColor Green' was printed to the screen (didn't actually change the color)
* nuget.exe was being put inside the src/ tree, moved to artifacts/Tools/nuget
* Temporary nuspec was created unnecessarily, now use -Properties instead of search and replace
* Downgraded to nuget 3.5.0 to workaround a perf issue in nuget 4.x pack
