Switch all projects to resolve references from package.config

Now projects should not list their references directly in the projects but instead in the packages.config and our ResolveNugetPackages build task will convert those to references for the project to build.

There are 2 projects Immutable and MetadataReader that still build using the portable profile instead of all packages and that is because they require specific contract reference versions. Right now we don't have packages for the specific versions yet but there are plans to do that as well and once that is done they can also build against packages.