Update nuget core

Resolves #52

Other things:

 - muted tests which are marked as NotImplementedException
 - muted `InstallManagerTests.EigenUpdateWithoutUpdateURL` which I need to resolve at some point in the future

TODO:

 - get this running through a CI server (ping @xpaulbettsx)

Open questions:

 - should I break up these tests into "unit tests" and "integration tests" for convenience sake?