Start abstracting use case logic and domain entities into a "Core" project.

[skittlz444]

So as to keep the use case implementations abstracted away from any UI framework dependent implementations (i.e. so that the controller action logic doesn't become dependent on react, blazor, mvc, or other ui specific framework).

This issue is specifically for setting up the core project, creating a demonstration use case for using MediatR and dependency injection to complete the required logic.

• Create the Core project
• Create a Core.Tests project
• Import MediatR into the projects
• Register MediatR
• Chose and implement a demonstration use case and tests