Changes:
* Add support for a property, `IsAspNetCoreApp`, in the .csproj file of assemblies which are part of the shared framework.
* Remove unused dependencies
* Remove reference which have become part of 'netcoreapp3.0'
Part of #4246
Changes:
* Update source code layout to follow the new conventions for this repo
* Update project files to use `<Reference>`
* Update targets to build NPM packages
* Update BuildTools to support custom 'restore' and 'test' targets