Feature loggingprovider

Adding concept of ILoggingProvider which can be added to ILoggerFactory

Creates a single default ILoggerFactory that does not need to be replaced to add 3rd party logging tech

Makes ILogging* interfaces AssemblyNeutral, and moves them into a standalone package
I'll check with them before merging, but we should [AN] things sooner rather than later if we think it'll cause problems