Articles/issue 390 configuration api v5

@dannycohen here we go :-) There are still a lot of grey areas, it is a first draft.

/cc @SimonCropp @johnsimons @indualagarsamy @SeanFeldman @sfarmar  please review and add comments to the missing parts.

Cheers
So, to clarify:
* the NServiceBus.Interfaces package is gone;
* IMessage and friends has been moved into NService.Core.dll
* the suggested way to go is the unobutrusive mode;
* if the user wants message interfaces can be used;

Correct?