Feature/assign virtual configs

[Schmluk]

• Adds assignment operators and constructors for virtual configs and other config structs.
• Natural initialization does not require specifying the type manually.
• NOTE: The above may fail if the same config is registered with different names. For now this behavior is supported but will warn the user. Could consider enforcing this to avoid issues in the future.
• Add utest for new functionality

@nathanhhughes This will break compatibility with the {Config, name} initialization, but I don't think we should support manually specifying the name in the future.

[nathanhhughes]

LGTM! fine with me to drop the type string arg / agree that it was kinda error-prone to have to specify it