[WIP] Chain route

This new route type allows to glue multiple routes together under a single route. This allows to address them with a single name. Common use-cases are:

* Connecting a path route with a scheme route (forcing HTTPS)
* Connecting a path route with a wildcard route
* Basically any case where you have "may_terminate = false" on the parent and only a single child

The route and factory is designed that way that it allows other modules to easily add conditions (like HTTPS) on a login route without changing the assembling structure.

This PR is so far feature complete, but yet lacks unit tests.