Make ClaimsMappingBuilder support inheritance

[alexeymarkov]

`interface IBaseCommand { string ContextId { get; set; } }

class MyCommand : IBaseCommand { string ContextId { get; set; } string Name { get; set; } }

.MapClaimToCommandProperty<IBaseCommand>("ContextId", x => x.ContextId) `

If you are agree that could be helpful I will provide a PR.

[JamesRandall]

That sounds useful - thanks.