Routing: Introducing unittests for core app router classes

This PR introduces a large chunk of unittests to document the behavior of the core application routing classes.

This was made possible through the generous donation of the people mentioned in the following link via an Indiegogo campaign: http://joomlager.de/crowdfunding/5-contributors
This conidition is unreachable. I couldn't find one situation where this could ever be true.