1. Reference a bunch of stuff from Nuget packages instead of VS.
2. Move to Update 2 versions of packages.
3. Now that we are using the packages, we're referencing
   Microsoft.VisualStudio.Shell.14.dll instead of .15 again.  This means
   that types that moved to Shell.Immutable.15 are not type forwarders.
   Luckily we didn't need anything from Shell.Immutable.15 in the project
   where it was a problem.