Unify test- and suite responder

The test and suite responder are much alike. Hence it makes sense to unify them. For this to work:
* the suite history formatter should only write a history when the executed page is a suite page.
* removed static failedCount from BaseFormatter. Now a custom listener can be registered on the ContextConfigurator.

Also:
* test summary fields are made private
* removed dead code from xml test formatter