Create FrameworkPackageSetting to set CurrentCulture and CurrentUICulture

[ChrisMaddock]

I'd like to add FrameworkPackageSetting for CurrentCulture and CurrentUICulture. These would allow the test thread cultures to be set at runtime, which can currently only be set by the [Set*Culture()] attributes at write-time.

This would make it easier for users to run the same test assembly under multiple cultures, and hopefully make testing under different cultures more accessible, and commonplace.

This is something I want to build on top of in the console/engine, once (if!) a package setting is added