Ugly error page when app/driver UI starting up

[cgreenhalgh]

If you install a new app or driver then the core UI allows you to navigate to the app/driver UI page once the container has started, which may be before the app's embedded webserver has started up. In this case the user will see an unformatted error page from the CM proxy.

This should either be prettier (e.g. with some guidance that the app may be starting up, try reloading, whatever) and/or the core UI could delay click through until the component confirms it is active (via the HTTP /status response).