To enable automatic restore of NuGet packages

Applied steps from following website to enable "Automatic Package
Restore" instead of "MSBuild-Integrated package restore" to solve issue
#20:

http://docs.nuget.org/docs/workflows/migrating-to-automatic-package-restore
Merge pull request #21 from solarpete/NuGet_auto_packet_restore

To enable automatic restore of NuGet packages, fixes #20