Invalid routes should error gracefully

[Adam Phillips]

Navigation to a nonexistent page can result in a HTTP 500 error. For example, visiting dockyard.com/campaigns/ errors and the Sentry capture is for a KeyError: key :campaign not found in: %{}

[AZholtkevych]

FYI @leandrocp

[Leandro Pereira]

Closed by #453 - it renders 404 since there's no page that matches that path and the error page will be dispu