Fix app manifest `redirects` property support fixes #685

The webapps actors isn't synced with webapps.jsm new feature.
We are (at least) missing `redirect` property support when installed a privileged app.
https://developer.mozilla.org/en-US/docs/Web/Apps/Manifest#redirects

Here is a simple fix for the simulator, but we should upstream this fix (and the other features we have added like receipts) and use the upstream version!

I also identified similar issue for CSP, but this time, we are missing upstream fixes... so I'll try to sync with upstream!