Upgraded all projects to use NuGet packages

As discussed in #56, all projects are now upgraded to use NuGet packages.

* For Moq 3.1.0.0 the closest version in NuGet is 3.1.416.3.
* For xUnit.net 1.6.1 the closest version in NuGet is 1.8.0.1549 were all tests could actually run and pass using the xUnit.net Runner for TestDriven.Net.
* For Rhino Mocks, FakeItEasy, and NSubstitute, the version remains the same.

Resolves #153.