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'
Replaces package references the following packages with local code:
Microsoft.AspNetCore.Certificates.Generation.Sources
Microsoft.Extensions.CopyOnWriteDictionary.Sources
Microsoft.Extensions.ClosedGenericMatcher.Sources
Microsoft.Extensions.ObjectMethodExecutor.Sources
Microsoft.Extensions.PropertyActivator.Sources
Microsoft.Extensions.PropertyHelper.Sources
Microsoft.Extensions.RazorViews.Sources
Microsoft.Extensions.SecurityHelper.Sources
Microsoft.Extensions.StackTrace.Sources
Microsoft.Extensions.WebEncoders.Sources