404 page on wrong path

Actual behavior: If you enter a wrong path, the app shell loads, but there is no activity in it.

Expected behavior: A 404 "page not found" page should be shown to the user.

added app-shell label

mentioned in commit 66f52864

assigned to @euneuber

This solution is very "lightweight" but translates on language changes.

TODO: styling. @BDF32E9143B2CD5B any suggestions?

mentioned in commit 019640da

added Review label

closed