3.0 no default routes

Part of #3693. This set of changes removes a few things:

* The default routes that CakePHP has historically shipped with. Instead app developers will be required to define the routes they want. This removal while a big change helps address the duplicate content issues that have come up many times in the past.
* `Routing.prefixes` is now gone.
* Automatic routes for plugins and prefixes are gone.

This set of changes also adds a new method to make it easier to connect 'fallback' routes. After this, I have one more set of changes for the Router to separate the collection + builder aspects of the current `ScopedRouteCollection` as I feel that class is doing two jobs and the current split of collection + router features is a bit gnarly.