Upgrade to .net core 2.1

Links to Razor Pages demo (from an MVC view, and from within an existing Razor Page to link to a sibling Razor Page).

Created RazorPage for populating database TODO items (to mirror controller). Extracted common Populate method to static class.

Removed RuntimeFrameworkVersion values hardcoded into projects so that the newest (i.e. 2.1) runtime would be used, to get rid of "System.Runtime 4.2.1.0 file not found" errors when running integration tests.

Remove DotNetCliToolReference elements for "Microsoft.AspNetCore", "Microsoft.VisualStudio", and "Microsoft.EntityFrameworkCore" packages (upgrade to 2.1 replaces these with global tools).

Added complete method and removed links to not existing actions.

And cleaning up some unused views.

Upgrade packages.

Update ToDoItemMarkCompleteShould

Adding Swagger

Adding Swagger

Changed Assertion to Single