Introduce relative_statistics to take loaded scenarios into account

[PragTob]

• fixes #287
• Sadly introduces another step into the verbose interface but there is really no other way to make it work with loading scenarios the way we want it to work... or well yeah there are other ways but this seems to be the nicest and even before I thought about doing it in a separate step and the code is also completely separate/easy to extract and tests are easier to setup. So I see this as a win.