To get the `WorldRoute` and `world` to work well with other components,
the `RouterComponent` needs to be on top.
This also fixes a small deprecation in the index.html file for the
examples.
This PR adds the `WorldRoute` which acts as a normal route, but instead
of adding a new component (page), it swaps out the world that the camera
(either the default camera or an explicitly passed in one) is watching.
