Add a flag that makes dispatch() return the response instead of send()ing it

[david]

Important for functional testing. Or maybe it should just always return the response, and the flag prevents it from being sent automatically?

[david]

(In [1811]) ability to prevent sending of the response in Controller::dispatch() which now also returns the final response (not the global one, mind you, but that one gets merged in) via parameter 'send_response'. plus some small refactorings. closes #469