Contoso University Vertical Slice App Updated to ASP.NET Core 3.0

To keep a running example of "how we do web apps", I've updated my Contoso University example app to ASP.NET Core 3.0. This sample app is just a re-jiggering of Microsoft's Contoso University Razor Pages sample app . It shows how we (Headspring) typically use: CQRS w/ MediatR Razor