Allow configuration to be overridden

Currently to configure a scenario you need to implement an interface and it ties configuration to the scenario author. From what I can see the only way to externally override configuration would be to use AOP. This isn't a very standard way of doing configuration. It should use public getter and setter methods so the configuration can be overridden or extended to, for instance, add in a scenario reporter.

Ideally I should be able to write a Sonar plug-in for JBehave that can run existing scenarios and capture their output for presentation within Sonar. To make this work for everyone out of the box, I shouldn't need to resort to using AOP or to requiring special per-scenario configuration by people who want to get nice reporting in Sonar.