Adding sanity checks in Route.

The controller(), method() and args() methods now check for null to
prevent Dispatcher overriding global defaults in the route() function
when $controller, $method or $args are null.
Dispatcher::addModule handles globals and prefix correctly.
Route throws Exceptions on getAction() failure.

When getAction() is called and the Route is untested or has failed, a
RouteUntestedException or RouteFailedException is thrown.
Cleaning up Config stubs in DispatcherTest.