Allow ScenarioClassLoader to instantiate scenarios using default constructor

Currently, all scenario classes need a constructor with a ClassLoader parameter, required by CLI runner with Maven and Ant.

While using core only, it is typically not required. So ScenarioClassLoader.newScenario() should support a varargs of parameter types, which also allow for no parameter types to instantiate using the default constructor. It is then up to the caller to use the appropriate parameter types.