Broaden the engine support to all namespaced controllers
Instead of trying to figure out if we're in an engine, the goal has
change to take the controller's class parents and use that as namespace
to the decorator. This has a few advantages. First, we're using the
Object as a parent by default which is equal has no parent (because of
the way ruby handles Constant hierarchy). Second, it allow you to wraps
decorators in the same manner you would with controller. It will give a
much more consistent experience between controller and decorators, which
was always the goal.