Don't show newtab notifications to managed users

Background

In #162 (closed) we added a new display method for opening a page in a new tab using the notification system. Since some managed users may encounter the first-run scenario each time the extension loads, this could be quite obtrusive. We don't want to outright ignore notifications though so we should just ignore newtab notifications for such users.

What to change

In lib/notificationHelper.js, ignore notifications with type "newtab" (i.e. don't add tab listener, don't open a new tab and mark as shown immediately) if browser.management.getSelf() returns installType === "admin".

See also related code from AdBlock.

Hints for testers

• Newtab notifications should not be shown to any managed users (i.e. users in large-scale deployments).
• Newtab notifications should be shown to any users who installed the extension through:
  • Extension store (e.g. Chrome Web Store)
  • Loading as unpackaged extension