Allow users to configure a list of routes that are exempt

This change allows users to configure additional admin routes. It is tested and works nicely. I considered removing routes that did not exist anymore on module uninstall or on route rebuild. Both options are fraught as we do not know why a route exists. Therefore I choose to not implement this and only check whether routes exist on save of the config form. Given then a non existing route in the config is harmless I think this is okay.

Automatically closed - issue fixed for 2 weeks with no activity.