macOS Support

[RLittlesII]

What does it take to implement admin privileges?

1. Assuming I can just override ISecurityPrincipal in Cupboard.Internal?
2. How do I execute in admin mode during a debug session?

Can we invert Cupboard so the mac version doesn't get dirty windows bits?

1. Ability to load cupboard dependencies based on platform
2. Maybe a registration module so you can load all of one platform's concerns vs another into the container?
3. Change the builder to have a Platform selector?
4. Have a builder per platform included?

Draft PR in progress

#50

Project consuming the new macOS bits

https://github.com/RLittlesII/Environment.Builder