Make "No Notifications" setting less broad, and fix a bug with default display behavior

Summary:
Fixes T12979. In D18457, we added a "No Notifications" setting to let users disable the blue and yellow pop-up notifications that alert you when an object has been updated, since some users found them distracting.

However, the change made "do nothing" the default, so all other JX.Notification callsites -- which never pass a preference -- were effectively turned off no matter what your setting was set to. This includes the "Read-Only" mode warning (grey), the "High Security" mode warning (purple), the "timezone" warning, and a few others.

Tweak things a little bit so the setting applies to ONLY blue and yellow ("object you're following was updated" / "this object was updated") notifications, not other types of popup notifications.

Test Plan:

• With notifications on in settings, got blue notifications and "Read-only".
• With notifications off in settings, got "Read-only" but no blue notifications.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T12979

Differential Revision: https://secure.phabricator.com/D18600