Support late apperances of routers

[nielslyngsoe]

This PR enables sub router-slots to render themself.

In the current version of code a sub router, is only triggered to render by the parent routers initiative.

This PR makes: a router, with no match, try to do the rendering on its connectedCallback. Making late appeared router-slots work.

[nielslyngsoe]

Hi @andreasbm

We would love to contribute to your package, but I see no activity at this moment.
Therefore we have chosen to close our Fork and continue our improvements for this package elsewhere.

If you return to maintaining this package, then let me know and I will open up PRs with the improvements that we have made.

Thanks for the good work.