APP_MANIFEST_REQUEST_FAIL is never emitted

[md-proteus]

App manifest failures, like 404s on app manifest retrievals, do not throw the expected AppHandler APP_MANIFEST_REQUEST_FAIL

[brianbaker]

@pc2459 do you remember anything on this one?

[pc2459]

What is says on the tin, really. If you were loading an app and manifests retrievals weren't 200 OK, you didn't get the APP_MANIFEST_REQUEST_FAIL AppHandler fired and so you couldn't react gracefully to the failure.