#18 Add Fluent Validation

[SimonGeering]

Closes #18

• Added Fluent validation package
• Added example validator, including custom predicate rule and use of property name replace term in custom messages
• Set-up DI for validator in the Domain.
• Added Unit Tests for the validator

This is not a full validator for CustomCommand. @benrick should create an issue for that defining bullet points for the validation rules to be enforced, then it can be picked back up at a later date. Rather this is intended as a POC to ensure the package is integrated into the codebase correctly.

Also, because it was annoying me:

An additional commit to removed he compiler warning about ASP.Net core, that was the result of the compiler failing to understand how we are hosting a web server in a WPF desktop app.

[SimonGeering]

Depends on how you want to expose the broken rules in the UI.

It should let you use it still as domain is referenced by UI and .net core does the thing that allows you to use assembly that are dependency of your direct dependency.

Should be able to expose it by implementing INotifyErrorInfo in the VM and have that delegate to the validation.